Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session NP11: Poster Session V: In-Person, Hall A (9:30-11:00am) and Virtual Poster Presentations (11:15am-12:30pm)
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Room: Exhibit Hall A and Online |
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NP11.00001: MFE: STELLERATORS Session Chairs: |
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NP11.00002: Auburn CTH and W7-X Research Progress and Plans David A Maurer, N. Bessard, D. A. Ennis, R. Dorris, T. Gonda, G. J. Hartwell, M. Kriete, J. C. Schmitt, E. Williamson, N. Allen The Compact Toroidal Hybrid (CTH) is a torsatron/tokamak hybrid. The main goals of the CTH experiment are to study disruptive behavior as a function of the applied 3D magnetic shaping, and to test and advance computational tools able to describe 3D MHD physics such as the V3FIT reconstruction code and NIMROD modeling of CTH. Recent density limit disruption, non-resonant divertor experiments, and hard x-ray generation studies will be overviewed and their relevance to tokamaks and quasi-axisymmetric stellarators will be discussed. Ongoing diagnostic development for the experiment includes development of new Hall probe array measurements, new spectroscopic studies of W and Ta, and coherence imaging of plasma flows. CTH also serves as a test bed for diagnostic development for our collaborations on the larger facilities like DIII-D and W7-X. Auburn research on W7-X will be summarized also. |
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NP11.00003: Calibration of a 3D Hall Probe Array for Equilibrium Reconstructions and MHD stability Studies in the Compact Toroidal Hybrid Noah P Bessard, David A Ennis, Gregory J Hartwell, David A Maurer Innovations in Hall sensor technology have led to the development of compact 3D sensors capable of measuring fields ranging from milli-Tesla to Tesla. An array of 8 of these sensors has been implemented as a magnetic diagnostic on the Compact Toroidal Hybrid (CTH) experiment. The array spans 45 mm allowing for simultaneous measurement of all fields within CTH at 8 positions. These local magnetic field measurements allow for improved knowledge of the current profile near the plasma edge using V3FIT reconstructions and will constrain the edge current gradient for MHD stability studies. The array has been calibrated on the benchtop using a 1-D Helmholtz coil, and in situ inside of CTH. Measurements demonstrate that effects from misalignment of the sensors’ internal components, and the planar Hall effect can both be neglected. Misalignment between the sensors making up the array was found to be less than one degree and can be accounted for. The CTH vacuum vessel and coil frames are also known to produce a measurable flux due to eddy currents that arise from their mutual inductance with the plasma current. After accounting for sensor misalignment and eddy currents, the experimentally reconstructed magnetic field profiles are in good agreement with profiles from a Biot-Savart model. |
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NP11.00004: Characterization and Mitigation of Runaway Electrons in the Compact Toroidal Hybrid Experiment Roger Dorris, David A Ennis, Gregory J Hartwell, David A Maurer The Compact Torodial Hybrid Experiment (CTH) at Auburn University has historically generated high X-ray dosages in the surrounding facility. The radiation profile has been characterized by correlation experiments using a pair of scintillators, which have measured X-ray energies in the range of 500 KeV to 10 MeV. It was determined that the X-rays are produced by runaway electrons which emit radiation from relativistic bremsstrahlung while trapped in confining magnetic fields at the end of the plasma discharge. The runaway electron populations and X-ray emissions have been studied across a range of CTH magnetic configurations with varying rotational transforms and field strengths. Variations in the magnetic configuration have been found to have a strong impact on runaway generation and the emission structure. Emission mitigation strategies have been developed and tested which minimize the runaway electron source, and have demonstrated that the X-ray production can be reduced over 90% by altering the magnetic surfaces and neutral gas feed post discharge. In addition, a method was developed which used the observed emission spectrum to model the performance of radiation shielding and inform shielding installation in the facility. Finally, a real-time X-ray monitoring system was installed to record and report future emissions. |
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NP11.00005: High-Resolution Ultraviolet Spectroscopy for Erosion Measurements of Tungsten and Tantalum Tomas Gonda, David A Ennis, David A Maurer, Gregory J Hartwell, Stuart D Loch, Nicholas R Allen, Connor P Ballance, Noah S Kim, Dane Z Van Tol, Curtis Johnson The erosion of Plasma Facing Components (PFC) in magnetically confined experiments can be quantified via a spectroscopic technique relating observed spectral line intensities to material influx via atomic physics coefficients (S/XBs). Failing to sufficiently resolve measured spectral lines due to impurity line blending, pressure broadening, and Zeeman splitting can lead to incorrect inferred erosion rates. A 1.33-meter focal length spectrometer has been outfitted with a high-resolution diffraction grating and a new UV optimized camera providing ~4 pm wavelength resolution down to 200 nm. Spectral data is collected by observing the plasma material interaction of a W or Ta Langmuir probe system installed on the Compact Toroidal Hybrid (CTH) experiment. Comparisons of new highly resolved W spectra to previous spectra reveals >20 previously unresolved or blended W spectral lines from 245 nm to 265 nm. High-resolution measurements of Ta emission in CTH are presented along with identifications in the visible and UV regions of Ta spectral lines for the potential benefit to erosion measurements. Initial calculations of Ta ionization cross-sections are utilized to estimate the ionization mean free path of Ta providing a preliminary comparison of expected Ta and W re-deposition rates. |
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NP11.00006: Design and Implementation of Langmuir Probe Arrays for Non-Resonant Divertor Studies in the Compact Toroidal Hybrid Experiment Nicholas R Allen, Roger Dorris, Kelly A Garcia, Aaron Bader, John C Schmitt, David A Maurer, David A Ennis, Gregory J Hartwell Modeling studies of the non-resonant divertor concept applied to the Compact Toroidal Hybrid (CTH) have shown a resiliency of the plasma strike lines to internal plasma currents. To this effect, two Langmuir probe (LP) arrays are being constructed for insertion into the non-axisymmetric plasma of CTH to validate the non-resonant divertor concept and measure the strike lines of 3D magnetic equilibria where the edge topology is altered by varying the internal plasma current. Both arrays will consist of ~10 probes spaced ~1 cm apart and will be positioned at both the half-field period and the limiting surface. The probes are located where the measured ion flux is expected to change as the plasma transitions from a limited LCFS to a stochastic boundary. The single-tipped LPs are constructed from 1 mm diameter molybdenum pins shielded by 5 mm diameter BN sleeves, and will be biased into the ion saturation regime with sampling rates of 500 kHz. CTH edge plasmas are expected to vary in density from 1017 to 1018 m-3 with electron temperatures of 5-10 eV. Initial experimental measurements of the edge plasma ion fluxes will be presented. |
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NP11.00007: Spectral measurements of neutral density in argon plasmas with widely varying fractional ionization Eleanor N Williamson, David A Maurer, Edward Thomas, Stuart D Loch, Saikat Chakraborty Thakur, David A Ennis, Curtis A Johnson, Jared C Powell, Gregory J Hartwell Understanding the region between fully ionized and neutral dominated plasmas is important to the study of the magnetosphere of the earth, the corona/chromosphere transition region of the sun, and detached divertors in fusion devices. Determining the fractional ionization of a plasma requires accurately measuring neutral density. We use an absolute intensity calibrated spectrometer coupled with results from a collisional radiative model to infer neutral argon density. Results will be shown from benchmarking spectroscopic measurements of neutral argon density against pressure in an RF generated magnetized plasma column between 0.1 to 2.0 mTorr at 0.1% fractional ionization. Preliminary results show that spectroscopic neutral density measurements agree with pressure-based neutral densities below 0.5 mTorr but do not increase proportionally with pressure measurements above 0.5 mTorr. Results `will be shown from the neutral density diagnostic in a higher fractional ionization experiment ranging between 10% and 70%. The general use of the diagnostic for neutral density measurements in argon plasmas is also discussed. |
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NP11.00008: Equilibrium reconstructions for Wendelstein 7-X with V3FIT John C Schmitt, Tamara Andreeva, Mark R Cianciosa, Joachim Geiger, Samuel A Lazerson, David A Maurer, Ulrich Neuner, Novimir A Pablant, Kian Rahbarnia, Jonathan Schilling, Henning Thomsen, Yuriy Turkin The present status of the V3FIT code for the free-boundary reconstruction of the magneto-hydrodynamic (MHD) equilibrium of W7-X plasmas with finite plasma pressure and toroidal current are presented. The reconstruction of the equilibrium is a vital tool for fusion experiments to model and interpret diagnostic signals. The iterative procedure involves solving the MHD equilibrium, calculating synthetic diagnostic signals and comparing the signals to those from the experiment. The parameters that describe the plasma position, boundary location and internal pressure and current profiles are adjusted until a 'best-match' is found between the synthetic signals and measured signals. Profile and parameter uncertainties are based on a best-linear estimate. The reconstruction output includes the shape and location of the plasma boundary, and profile information of the plasma parameters. This set of information is then used to interpret diagnostic signals and can be used for further analysis of the equilibrium state. Typically, the MHD solution is provided by VMEC, which only permits nested closed flux surface. The SIESTA code, which is already coupled with V3FIT, permits islands to be present in the free-boundary MHD solution. |
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NP11.00009: Effects of drifts on scrape-off layer transport in the W7-X stellarator David M Kriete, Arun Pandey, Valeria Perseo, John C Schmitt, David A Ennis, Dorothea Gradic, Kenneth C Hammond, Marcin Jakubowski, Carsten Killer, Ralf König, David A Maurer, Felix Reimold, Victoria Winters A key mission of the W7-X stellarator is developing the physics basis of the island divertor heat exhaust concept. To investigate the effects of drifts on transport in the island divertor scrape-off layer (SOL), plasmas with matched upstream parameters but oppositely directed magnetic fields, and therefore oppositely directed drifts, are compared. At low density (ne < 2 × 1019 m-3), C2+ flows measured by coherence imaging spectroscopy (CIS), which are a good proxy for the main ion flows, are near-unidirectional throughout the SOL and reverse direction upon field reversal. The divertor Langmuir probes (LP) measure a density asymmetry between upper and lower targets that also reverses with field direction. These observations are in qualitative agreement with a simple SOL particle and momentum transport model that includes the poloidal E × B drift. The model predicts the flow stagnation point to shift from the geometric center between targets to the X-point in the direction of the drift, thereby producing the observed unidirectional flow pattern. Both CIS and LP measurements indicate the drift velocity is ∼100 m/s at low density. As density increases, drift effects rapidly diminish in the island SOL but persist in the regions shadowed by divertor targets. |
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NP11.00010: A New Coherence Imaging Spectroscopy Diagnostic Optimized for Ion Temperature Measurements in the W7-X Scrape-Off Layer David A Ennis, David M Kriete, Dorothea Gradic, Valeria Perseo, Tomas Gonda, Ralf König, David A Maurer, Saikat Chakraborty Thakur, Edward Thomas, W7-X Team To investigate scrape-off layer (SOL) physics in the island divertor of the W7-X stellarator a new coherence imaging spectroscopy (CIS) diagnostic is being optimized for ion temperature measurements. The CIS technique provides high-spatial-resolution measurements of ion velocity in the SOL of W7-X but ion temperature measurements are challenging due to the contribution of Zeeman splitting at high magnetic fields (B ~ 2.5 T). A technique is described for estimating the uncertainty in the ion temperature due to the spatial variation of emission along the CIS lines of sight. The impact of bremsstrahlung radiation on CIS measurements may be substantial for high-density ( > 1 × 1020 m-3) W7-X plasmas. A design is presented for the new W7-X CIS instrument that utilizes multiple birefringent crystals and a micropolarized camera in a multi-delay configuration to provide more accurate ion temperature measurements. The birefringent crystals have been optimized to minimize sensitivity to Zeeman splitting while maintaining sufficient sensitivity to ion temperature. The new multi-delay CIS instrument has been tested on the Magnetized Dusty Plasma Experiment (MDPX) to quantify the contribution of Zeeman splitting over a range of magnetic fields relevant for W7-X measurements. |
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NP11.00011: Helical coil stellarators with good outboard side access Todd M Elder, Allen H Boozer, Elizabeth J Paul A helical-coil stellarator configuration is presented using the HSX plasma surface. The bulk of the vacuum magnetic field should be produced by two helical coils which pass near the plasma on the inboard side at the helical twist of the plasma surface and pass far away on the outboard side of the plasma. This configuration would offer numerous benefits: (1) the large outboard side coil-plasma gap allows (a) easy access to the plasma chamber, (b) room to install plasma diagnostics and breeding blankets, and (c) easy field modification using trim coils, (2) the simplicity of coil production for an optimized stellarator plasma, and (3) toroidal ripples can be reduced since the helical coil is continuous. To achieve this coil design we will use adjoint REGCOIL1 using a combination of guesses for the winding surface guided by low aspect ratio analytic theory and a regularization function which encourages solutions with concentrated current densities located far from the plasma surface on the outboard side. |
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NP11.00012: Stabilisation of electrostatic electron-temperature-gradient instability in stellarators Jason F Parisi, Felix I Parra, Michael Barnes, José Manuel García Regaña, Iván Calvo, Michael Hardman, Tony Qian, Denis A St-Onge, Grzegorz Walkowski We use the gyrokinetic code \texttt{stella} [Barnes, 2019] to study electron-temperature-gradient (ETG) instability [Dorland, 2000] in a W7-X discharge (20013) [Gonzalez, 2022] and a LHD discharge (113208). Linear electrostatic stability analysis reveals that microinstabilities, including ETG instability, in LHD are stabilized at kyρe << 1, while W7-X is strongly unstable to ETG modes from kyρi ~1 to kyρe >> 1. Here, ky is the binormal wavenumber, and ρe and ρi are the electron and ion gyroradii, respectively. We show that the stabilization of ETG instability in LHD is due to desirable properties of the magnetic geometry: specifically, in LHD (but not in W7-X) the electron magnetic drift frequency is fast compared with the ExB drift frequency, which results in weak toroidal ETG instability [Parisi, 2020]. Because stellarators typically have a large aspect ratio, the ratio of the major radius to the temperature gradient length scale, R/LTe, is large. This large value of R/LTe results in linear ETG modes with perpendicular wavenumbers that are much larger than their binormal wavenumber, and are challenging to resolve numerically. Such ETG modes are ubiquitous in the W7-X discharge we study. The relative stability of LHD to electron-gyroradius-scale instability suggests a path to stabilizing turbulence in stellarators with magnetic geometry. |
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NP11.00013: Magnetic turnstiles of a new type of stellarator divertor – the hybrid stellarator divertor Alkesh Punjabi, Allen H Boozer A new type of stellarator divertor is discovered. It has properties of both the island divertor and the nonresonant divertor. For this reason, we have called it hybrid divertor. This new divertor has some desirable properties [see http://meetings.aps.org/Meeting/DPP20/Session/BP14.18] which are of practical value. The field lines from just outside the outermost confining magnetic surface reach the wall through magnetic turnstiles. Magnetic turnstiles always come in a pair of magnetic flux tubes – an outgoing flux tube and an incoming flux tube. This is because magnetic field is divergence-free. The outgoing flux tube carries magnetic flux from just outside the outermost surface, and the incoming tube carries the flux from the wall to just outside the outermost surface. We have calculated the full 3D magnetic turnstiles of the hybrid divertor using the method developed in [A. Punjabi and A. H. Boozer, Phys. Plasmas 29, 012502 (2022)]. We have found that there are three magnetic turnstiles in hybrid divertor. All three are adjoining turnstiles. This means that the magnetic flux tubes of each of these three turnstiles start at adjoining locations just outside the outermost surface. We have also calculated the probability exponents of these three magnetic turnstiles in hybrid divertor using the method developed in [A. H. Boozer and A. Punjabi, Phys Plasmas 25, 092505 (2018); A. Punjabi and A. H. Boozer, Phys. Plasmas 27, 012503 (2020) (Editors Pick)]. We have found that the probability exponents are 2.21, 2.25, and 4.43]. This work is supported by DOE OFES grants DE-SC0020107 to Hampton University, and DE-FG02-03ER54696 to Columbia University. Research used resources of the NERSC, supported by the Office of Science, US DOE, under Contract No. DE-AC02-05CH11231. |
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NP11.00014: Global gyrokinetic simulations of electrostatic microturbulent transport using kinetic electrons in LHD stellarator Tajinder Singh, Javier H Nicolau, Zhihong Lin, Sarveshwar Sharma, Abhijit Sen, Animesh Kuley Drift wave instabilities responsible for the electrostatic turbulence transport in fusion plasma, namely, the ion temperature gradient (ITG) and trapped electron mode (TEM), are studied using gyrokinetic toroidal code (GTC) in the LHD stellarator. The ITG turbulence simulations with kinetic electrons show that the kinetic effects increase the growth rate of the most dominant eigenmode by ~1.5 times and the turbulent transport by ~2.5 times as compared to the case with adiabatic electrons. The zonal flow regulates the ITG turbulence transport by reducing it by almost two-folds and hence acts as a dominant saturation mechanism. The linear TEM simulations show that the electrostatic potential is localized on the low magnetic field region where the curvature is bad, just like ITG turbulence. The nonlinear TEM turbulence simulations show that the main saturation mechanism is not the zonal flow but the inverse cascade of the high poloidal and toroidal harmonics to the low harmonics. The comparison of nonlinear simulations with different pressure profiles indicates that the ITG turbulence is more effective in driving heat conductivity whereas the TEM turbulence is responsible for the particle diffusivity. |
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NP11.00015: Merging of the superbanana plateau and √ν transport regimes in nearly quasisymmetric stellarators. Peter J Catto, Libby Tolman, Felix I Parra Alpha particle confinement is one of the most demanding issues for stellarators. Here the collisional confinement of barely trapped alphas in an optimized stellarator is considered by accounting for the resonance due to tangential drift reversal and investigating the sensitive role of magnetic shear in keeping this resonance close to the passing boundary in some nearly quasisymmetric stellarator configurations. The treatment relies on a narrow collisional boundary layer formulation that combines the responses of both these resonant pitch angle alphas and the remaining barely trapped alphas. A novel merged regime treatment leads to explicit expressions for the energy diffusivity for both superbanana plateau (or resonant plateau) and √ν transport in the large aspect ratio limit for a slowing down tail alpha distribution function, where ν is the pitch angle scattering collision frequency of the alphas off the background ions. |
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NP11.00016: Designing a Permanent Magnet Stellarator Djin Patch Models show that optimized stellarator plasma boundaries can be achieved with permanent magnets and circular planar coils. MUSE, a tabletop stellarator being assembled at PPPL, promises to show excellent quasi-symmetry and achieve very low effective ripple, through the use of 16 planar coils and about 10,000 neodymium magnets. MUSE is designed to be as simple as possible. MUSE has a vacuum vessel with a circular cross-section, a major radius of 30cm, and a constant minor radius of 7.5 cm. It also has a toroidal field of .15T, andrectangular prism magnets with discrete sizes that are both physically and magnetically oriented normal to a circular cross-section torus. These features make it as simple as possible. Allowing for a more complex design increases the engineering difficulty, but it also increases the design space of the types of equilibria that are achievable. This poster will discusses MUSE's approach to the iterative process of finding an arrangement of permanent magnets that meet their plasma and engineering constraints, it will discuss the lessons learned from the physical assembly of MUSE, as well as next-step stellarator designs and approaches, including Landreman and Paul's recent "PreciseQA". |
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NP11.00017: Computation of linearly unstable resistive MHD modes in tokamak and stellarator plasmas using NIMSTELL Sanket A Patil, Carl R Sovinec, Chris C Hegna Calculating the nonlinear MHD behavior of stellarator plasmas on resistive timescales is important for understanding and predicting soft beta limits and loss of equilibrium. The code NIMSTELL [1] has been developed with these goals in mind. It uses a finite-element grid in the poloidal plane, and Fourier series in a generalized toroidal angle for all perturbations and steady-state fields, including the physical coordinates (R, Z, φ). An interface between NIMSTELL and DESC [2], a 3D ideal MHD equilibrium code, has been developed for obtaining flux-aligned finite-element grids and the corresponding equilibrium fields. As a first step toward nonlinear calculations, linearized visco-resistive MHD equations have been solved using NIMSTELL. Benchmarking against NIMROD has been completed for tearing modes in a circular tokamak. Here, we investigate tearing in a toroidal plasma with a helically twisting elliptical cross section of eccentricities ranging from 0.4 to 0.8. First results for the linear MHD stability of a set of QHS configurations [3] are also presented. |
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NP11.00018: Single Stage Coil/Plasma Optimization with DESC Rory Conlin, Jonathan Schilling, Daniel W Dudt, Dario Panici, Egemen Kolemen We present recent upgrades to the DESC code for single stage optimization of both coils and free boundary 3D MHD equilibria. A spectral collocation approach is used to compute the boundary error, which avoids the need for inverting large matrices to compute the vacuum potential, and doing all calculations in real space allows for efficient handling of the singularity in the Biot-Savart kernel. We demonstrate solutions of both vacuum and finite beta equilibria and compare to both field line tracing and legacy codes such as VMEC, and show configurations optimized for metrics including quasi-symmetry, magnetic well, coil complexity, and fast particle confinement. |
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NP11.00019: Energetic particle optimization of quasi-axisymmetric stellarator equilibria Alexandra LeViness, Aaron Bader, Benjamin Faber, Kenneth C Hammond, Samuel A Lazerson, John C Schmitt, David A Gates An important goal of stellarator optimization is increasing confinement of energetic particles, such as those born from fusion reactions in a reactor. In this work, the fixed-boundary stellarator equilibrium LI383 was optimized for energetic particle confinement via a two-step process using the stellarator optimization code suite STELLOPT. In the first step, the equilibrium was optimized for high quasi-axisymmetry (QA) on a single flux surface near the mid-radius, and in the second, a minimization of the analytical quantity ΓC was performed while maintaining the improved quasi-axisymmetry. This process was performed multiple times on the same initial equilibrium, resulting in a group of equilibria with significantly improved energetic particle confinement, as demonstrated by Monte Carlo simulations of fusion alphas in scaled-up versions of the optimized equilibria. This is the first successful attempt to improve energetic particle confinement in a QA stellarator by optimizing ΓC. Finally, a statistical analysis was performed, examining the relationship between energetic particle losses and analytical metrics such as QA error and ΓC. In particular, ΓC was strongly correlated with losses, with a nearly linear relationship between volume-averaged ΓC and particle losses after 1 ms. |
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NP11.00020: Exploring stellarator beta-limits with nonlinear MHD modeling Adelle Wright, Nathaniel M Ferraro We present the first results from a parametric exploration of beta-limits in a 10-field period heliotron, showcasing the M3D-C1 code’s new capability to perform extended-MHD simulations in stellarator geometry. We examine the effect of heating power and transport on MHD dynamics and nonlinear stability, observing low-n core mode activity that is broadly consistent with experimental observations on the Large Helical Device (LHD). This paves the way for quantitative validation with LHD experiments. |
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NP11.00021: Construction of MUSE Permanent Magnet Stellarator and Error Field Measurement Using Electron Beam Mapping Xu Chu, Tony Qian, Michael Zarnstroff, Bruce Berlinger, Christopher Pagano, Djin Patch, Dominic Seidita, Mohammed Haque, Arturo Dominguez
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NP11.00022: Minimal Poincare Boundary Condition for 3D Ideal MHD Equilibria in DESC Dario Panici, Rory Conlin, Daniel W Dudt, Egemen Kolemen We present a minimal Poincare boundary condition for solving 3D MHD equilibria, which is implemented in the DESC stellarator optimization code[1-4]. The fixed-boundary problem is often solved by specifying a toroidal surface as the LCFS BC, however, one can also specify a 2D toroidal cross-section as the BC and view the problem as a BVP in the toroidal angle as opposed to the radial coordinate. This approach is implemented in DESC, and offers new insights on uniqueness, as well as aid in optimization by reducing the number of variables required to represent the boundary. Results with this approach will be shown and compared to the conventional LCFS boundary method. A new metric for nested surfaces is also shown, based on the idea of re-solving a fixed boundary equilibrium using inner flux surfaces as the LCFS and comparing the resulting solution to the original equilibrium. |
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NP11.00023: Energetic particle loss mechanisms in reactor-scale equilibria close to quasisymmetry Elizabeth J Paul Collisionless physics primarily determines the transport of fusion-born alpha particles in 3D equilibria. Several transport mechanisms have been implicated in stellarator configurations, including stochastic diffusion due to class transitions, ripple trapping, and banana drift-convection orbits. Given the guiding center evolution in a set of six quasihelical and quasiaxisymmetric equilibria, we perform a classification of trapping states and transport mechanisms. In addition to banana drift convection and ripple transport, diffusive banana tip motion associated with the non-conservation of the parallel adiabatic invariant is substantial among prompt losses, especially in quasiaxisymmetric equilibria. Furthermore, many lost trajectories undergo transitions between trapping classes on longer time scales, either with periodic or irregular behavior. We discuss possible optimization strategies for each of the relevant transport mechanisms and perform a comparison between classified guiding center losses and recently-developed metrics for banana drift convection transport. Equilibrium characteristics responsible for distinctions in transport are discussed. Quasihelical configurations are found to have natural protection against both ripple trapping and diffusive banana tip motion. |
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NP11.00024: Stellarator Linking Axisymmetric Mirrors (SLAM) Tony Qian, Xu Chu, Henry Fetsch, Dingyun Liu, Richard Nies, Jason Parisi, Adam Rutkowski, Jacob A Schwartz, Charles P Swanson This poster motivates the study of using optimized stellarators to link large volume axisymmetric mirrors. |
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NP11.00025: Preferred Magnetic Axes For Optimal Quasi-Axisymmetry Wrick Sengupta, Eduardo Rodriguez, Richard Nies, Elizabeth J Paul, Stefan Buller, Matt Landreman, Amitava Bhattacharjee Recently, enormous progress has been made in obtaining quasisymmetry (QS) of outstanding precision through numerical optimization. Significant analytical progress has also been made possible thanks to the asymptotic expansions near the magnetic axis (NAE). A critical factor in realizing good QS through the second-order of the NAE is the choice of the magnetic axis. However, because of the complexity of the second-order NAE equations, analytical characterization of these preferred magnetic axes for optimal QS has not been possible so far. In this work, we shall attempt to answer this question for quasi-axisymmetric (QA) systems. We show that the magnetic axis is well described for small rotational transforms by the same equations that govern Euler-Kirchhoff elastic rod centerlines (Langer and Singer, SIAM review 1996, Pfefferlé et al. PoP 2018). Surprisingly, the connection to these equations can only be made partially within the NAE framework and requires several concepts from the soliton theory. We shall present analytical and numerical evidence supporting our insights for a broad range of QA stellarators. |
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NP11.00026: Update on the W7-X phase contrast imaging diagnostic for OP 2 experiments Eric Edlund, Miklos Porkolab, Jan-Peter Bähner, Olaf Grulke, Søren Kjer Hansen, Adrian von Stechow Recent experiments in high performance stellarator plasmas, such as W7-X, indicate that turbulence plays a dominant role in determining the transport of energy and particles [1]. A wide range of instabilities, including ITG and TEM modes can produce turbulence across a wide range of temporal and spatial scales. The W7-X phase contrast imaging (PCI) diagnostic is capable to measure turbulent density fluctuations with a bandwidth of 2 kHz to about 500 kHz, with higher frequency fluctuations detectable at lower signal levels, and a wavenumber range spanning 1.5 cm-1 to 10 cm-1, depending on the optical configuration used [2]. The implementation of water-cooled divertors in W7-X imposed major changes to the diagnostic system for the OP 2 campaign. This presentation will review the recently upgraded PCI diagnostic, its measurements capabilities, and an optical heterodyne upgrade that will create the possibility of ICRF wave detection. Some representative measurements from the OP1.2 experiments and the OP2 experiments, if available, will also be presented. |
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NP11.00027: Verification and validation of neoclassical predictions of fast-ion distribution functions in gyrokinetic simulations Wataru H Hayashi, William W Heidbrink, Zhihong Lin, Javier H Nicolau, Masaki Nishiura, Yasuko Kawamoto, Kunihiro Ogawa, Tetsutaro Oishi, Ryohsuke Seki, Hideo Nuga, Hiroyuki Yamaguchi, Masaki Osakabe, Christopher M Muscatello Fast ion distribution functions for MHD-quiescent plasmas in the Large Helical Device (LHD) are compared to neoclassical predictions. Fast ion D-alpha (FIDA) data and heavy ion beam probe (HIBP) data were collected during the 23rd LHD campaign for configurations with varying major radii. Variations in the major radius are shown to have an effect on the neoclassical confinement of fast ions. The experimental FIDA signals are compared to spectra generated by the fast ion diagnostic simulation code FIDASIM with inputs for the distribution function created by the gyrokinetic toroidal code (GTC). Distribution functions from GNET are also used for benchmarking GTC. Additionally, radial electric field profiles collected by the HIBP are compared to the calculated electric field from GTC. |
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NP11.00028: Figures of Merit for Plasma-Coil Separation of Stellarators Jonathan Kappel, Matt Landreman Stellarator reactor size is limited by the separation between the outer boundary of the plasma and the external coils that produce a confining magnetic field. This is because at least 1 meter of additional components, such as breeding blankets and shielding, are required in between the plasma and the coils. Understanding the nature of this plasma-coil separation may unlock a deeper insight into why some stellarator configurations prove difficult to create coil shapes for. Here, we explore the hypothesis that largest distance between the coils and the plasma is bounded around the shortest scale length of the magnetic field, as expressed by the ∇ B tensor. We explore the relationship between the plasma-coil separation and the ∇ B scale length using the regularized current potential method REGCOIL. Compared to other coil optimization tools, REGCOIL’s sheet current approach means the objective function guiding the coil shapes can be minimized without local minima. Further development of the ∇ B scale length as a heuristic for the plasma-coil separation may allow for this separation to be maximized within plasma equilibrium design to create configurations with larger plasma-coil separations.
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NP11.00029: Analytical and simulation feasibility study for an ion cyclotron resonance heating (ICRH) antenna for the TJ-II stellarator. Debjyoti Basu, Alexander V Melnikov, Philipp O Khabanov, Mikhail A Drabinskiy The TJ-II Stellarator is a machine with low magnetic shear with four periods, major and minor radii 1.5m, 0.22m, operating at BT≈ 1T, with hydrogen plasmas in the density range n ≈ 0.3×1019- 5×1019m-3 and electron temperatures Te=900-300eV with corresponding Ti=80-150eV for low-density plasmas without NBI and high-density plasmas with hydrogen NBI. TJ-II is equipped with two gyrotrons (53.2GHz, 300kW each), used for plasma startup with ECRH electron heating and one NBI system of 1.2MW, aimed at ion heating and fast particle physics study. Recently, an ICRH system has been proposed to heat the ions more efficiently. To develop an ICRH system in TJ-II, an analytical study and a simulation have been undertaken to determine the best ion cyclotron range of frequencies and ICR heating scenario for the whole density range using experimentally obtained density and magnetic field profiles. Heating of single species plasmas with second harmonic ion heating and two species plasmas with minority and hybrid ion heating are considered. A two- and three-strap ICRH antenna design is under study and the simulations are carried out with COMSOL Multiphysics. The analytical and simulation results will be presented. |
Author not Attending |
NP11.00030: A Comparison of VMEC, SIESTA and SPEC Equilibria Andrew S Ware, Priya Keller, Michael Couso, Stuart R Hudson The numerical calculation of three-dimensional MHD equilibria is an essential step in designing and analyzing toroidal magnetic confinement devices. The type of equilibrium is determined by the assumptions used in designing the code that calculates the equilibrium. The VMEC code is an Ideal MHD code that assumes nested toroidal flux surfaces [S. P. Hirshman and H. K. Meier, Phys. Fluids 28, 1387 (1985)] and it has been widely used in stellarator and tokamak physics. The SIESTA code relaxes the assumption of nested toroidal flux surfaces and switches between Ideal and Resistive MHD in the process of searching for an equilibrium [S. P. Hirshman, R. Sanchez and C.R. Cook, Phys. Plasmas 18, 062504 (2011)]. The SPEC code is designed with the concept of multi-region, relaxed MHD [S. R. Hudson, et al., Phys. Plasmas 19, 112502 (2012)]. In this work, these three codes are used to calculate tokamak and stellarator equilibria, with a comparison of the differences and similarities of the results. The focus here will be on obtaining equilibria from each of the different codes for the same equilibrium. The challenges and limitations of the codes will be discussed. |
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NP11.00031: Designing Non-Resonant Divertors Aaron C Bader, Kelly A Garcia, Benjamin Faber, Heinke G Frerichs, John C Schmitt Non-resonant divertors for stellarators do not rely on the presence of edge islands and are therefore a possible divertor solution for configurations that have substantial bootstrap current. Previous work has examined simple wall structures by uniformly expanding the plasma last closed flux surface. It was shown that the strike line positions at the wall is resilient to changes in the plasma boundary shape on the order expected from bootstrap current evolution [1]. In this work we show how it is possible to increase the distance between the divertor plates and the plasma. Increasing the distance is desired to improve divertor closure and to increase neutral pumping efficiency. We determine the limits both of the divertor/plasma distance, and the limits of divertor closure. We provide a simple agorithm for a non-uniform expanded divertor, based off of the flux surface expansion at the plasma boundary. Using this algoritm and results from simple field-line following with field-line diffusion, we show the maximum allowable expansion for various configurations. Once the maximum expansion is determined, resiliency can be checked by perturbing the boundary. We use EMC3-EIRENE simulations to calculate the neutral pressure. |
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NP11.00032: Optimizing Trapped Electron Mode Stability in Quasi-Symmetric Stellarators Joey M Duff, Benjamin Faber, Chris C Hegna, M.J. Pueschel, Paul W Terry An important goal of stellarator optimization is to find stellarator configurations with reduced turbulent transport using three-dimensional (3D) shaping. Trapped electron mode (TEM) turbulence is thought to play a prominent role in the confinement properties of quasi-symmetric stellarators [1]. One method for improving the turbulent transport properties of tokamak plasmas is to appeal to negative triangularity. This improvement is in part attributed to precessional drift reversal of trapped electron orbits. In this work, we attempt to use negative 'helical' triangularity as a mechanism to reduce TEM turbulence in quasi-helically symmetric stellarators. A new optimization framework is developed using local 3D MHD equilibrium solutions [2]. Optimization studies using local 3D MHD solutions have successfully found configurations with improved quasi-symmetry. In this work, we use optimization of local 3D MHD solutions to improve TEM stability. The gyrokinetic code GENE is used to assess the local TEM linear stability characteristics. These insights help improve metrics for modeling TEM turbulence in ensuing optimization calculations. |
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NP11.00033: A novel table-top stellarator experiment at UW-Madison - parameters and design Thomas Gallenberger, Benedikt Geiger, Michael J Gerard, Ryan Albosta, John C Schmitt, Benjamin Faber A new table-top stellarator experiment has been designed for UW Madison using one helical coil and one planar coil to produce a five-period symmetric magnetic field structure with quasi-poloidal symmetry in the core. The effective major and minor radii of the plasma are 19 cm and 1.8 cm, respectively, translating to an aspect ratio of 10.7. The torsatron coil design employed here minimizes Lorentz forces on the coil enabling the coil supports to be 3D printed from plastic. Considering currents of up to 10 kA, a core magnetic field of 0.08 T can be achieved with a maximum linear force density of only 5 N/cm on the coils. VMEC equilibrium reconstructions show that the two coils generate a rotational transform of up to 0.12 with an effective magnetic ripple of 0.1 which will provide reasonably good neoclassical confinement. First estimates of the performance of the new experiment using the ISS04 scaling and 200 W of absorbed 2.45 GHz ECRH suggest that core electron temperatures of about 40 eV can be reached which translates to a normalized electron gyro-radius of about 0.01. |
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NP11.00034: Exploring Features of Non-Resonant Divertor Design at the Compact Toroidal Hybrid (CTH) Kelly A Garcia, Aaron Bader, Heinke G Frerichs, Nicholas R Allen, Jonathan M Van Blarcum, Gregory J Hartwell, John C Schmitt, Oliver Schmitz Non-resonant divertors (NRD) separate the confined plasma from surrounding material structures with the resulting boundary region rendered by a chaotic magnetic edge structure. This edge structure is formed by interacting magnetic islands and is eventually guided to wall elements such that the field lines end in rigid strike lines. The Compact Toroidal Hybrid (CTH) can serve as a test-bed for NRD solutions. The background field coils and the ohmic current drive system of CTH are used to alter the rotational transform between 0.3 < ι < 0.75. We show the presence of the chaotic edge field line structure which evolves with current and is connected to the wall through stable trajectories that yield strike lines. These chaotic structures define the plasma edge transport towards the wall – an interplay that we aim to explore. We calculate strike point locations for the exiting plasma for multiple ohmic current values. The calculated strike point locations enable us to design and numerically test an instrumented divertor plate for CTH which can then be used to experimentally measure NRD resiliencies with respect to equilibrium changes. The test plate in CTH is designed to be movable along a radial axis and can act both as a limiter, when fully extended, and as a divertor when placed outside the LCFS. We present results from both field-line calculations and EMC3-EIRENE fluid Monte-Carlo simulations of the edge behavior in the vicinity of the CTH test plate for various configurations and different plate positions. |
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NP11.00035: Exploration of Ion Heat Pulse Propagation Experiments in W7-X Benedikt Geiger, Oliver Ford, Marc Beurskens, Gavin M Weir, Samuel A Lazerson, Sergey Bozhenkov, Benjamin Faber, Shawn Simko, Peter Poloskei Understanding and control of turbulent transport in high temperature plasmas is one of the most important topics of fusion energy science as turbulence degrades the plasma performance above critical gradient lengths. To study the corresponding stiffness of heat transport, i.e. to analyze how strong heat fluxes increase with the normalized temperature gradient length, power modulation studies are a commonly applied technique for the electron channel [1] but similar studies considering the ion channel have hardly been performed. Here, we present the design and concept of a new high speed ion temperature diagnostic for W7-X, as well as numerical tools developed to perform ion heat pulse propagation studies using neutral beam injection (NBI) modulation. Moreover, first results obtained during the previous experimental campaign are discussed which lack fast enough ion temperature measurements but show a clear impact of NBI modulation on the electron temperature profile. |
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NP11.00036: Reduced turbulent transport in quasi-helically symmetric stellarators Chris C Hegna, Benjamin Faber A distinctive feature of quasi-helically symmetric (QHS) stellarators is their relatively small connection length. This has several beneficial MHD consequences including reduced Pfirsh-Schlüter and bootstrap currents and smaller Shafranov shifts relative to equivalent scale tokamaks at comparable plasma beta. In this work, we argue that the shorter connection lengths of QHS will also lead to superior turbulent transport properties. While QHS stellarators tend to have larger normalized growth-rates relative to other configurations due to reduced connection length, nonlinear gyrokinetic simulations show that QHS stellarators have net lower turbulent heat transport than other optimized stellarator options[1]. We argue the appropriate spatial scale for ITG-like turbulence is set by the banana width. Following this logic for conventional stellarators, one can produce stellarator energy confinement time scaling laws that are remarkably consistent with the empirically derived ISS04 scaling. The reduced banana widths present in QHS stellarators imply that the reduced connection length has a net beneficial effect on turbulent transport. Nonlinear gyrokinetic simulations are performed in support of this premise. |
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NP11.00037: Minimizing Magnetic Island Width Sensitivity to Multi-Filament Coil Shape Perturbations Thomas G Kruger, David T Anderson, Aaron C Bader, Chris C Hegna, Caoxiang Zhu Stellarator coil optimization attempts to reconstruct magnetic fields from fixed-boundary equilibria. These reconstructions are typically not perfect and there will be differences between the fixed and free-boundary equilibria. Resonant error fields can induce considerable magnetic islands, even if the magnitude of the error fields is small. These islands typically degrade energy confinement times. Methodologies for minimizing island widths have been implemented with respect to NCSX and CTH. Here we introduce a new method to minimize the island width by targeting the island's helical flux. However, optimizing for island widths alone is insufficient due to the islands being extremely sensitive to magnetic field perturbations, therefore we must consider the island widths' sensitivity to coil shape perturbations. Due to the high island width sensitivity, we optimize realistic coil windings (multi-filament coils). We calculate the island width sensitivity to coil shape perturbations and two methodologies for minimizing island width sensitivity are presented. The first method is to target the magnitude of the coil shape gradient for the helical flux. We also demonstrate a more robust method, that is, a stochastic optimization of the helical flux. |
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NP11.00038: Data analysis for the upgraded Thomson Scattering diagnostic in HSX Zander N Keith, Wayne Goodman, David T Anderson A data analysis code has been developed to calculate a joint PDF for electron temperature and density using Thomson Scattering (TS) in the Helically Symmetric eXperiment (HSX). The upgraded TS diagnostic features 1.25GS/s digitizers and newly designed high speed electronics that give a time-resolved pulse signal with significantly reduced noise and minimized deformation. This allows the use of curve fitting techniques to reduce uncertainty and improve accuracy of the resulting measurements. The PDF for electron temperature and density will be used in a future integrated data analysis (IDA) system that combines multiple diagnostics for higher fidelity profiles. A sensitivity analysis has been performed using Matlab and Simulink to predict how the system will function over a range of plasma parameters expected in the HSX upgrade, as well as determining the effects of noise sources on the calculated electron temperature and density values. |
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NP11.00039: Experimental program and plans for HSX upgrade Santhosh T Kumar, David T Anderson, Aaron Bader, Benedikt Geiger, Chris C Hegna, Konstantin M Likin, Joseph N Talmadge The HSX stellarator is currently undergoing a major upgrade. A new 70 GHz gyrotron will be installed that will provide up to 300 kW of power for up to 100 ms. This upgrade will allow operation at three times higher plasma densities (up to 2.0x 1019/m3) with an ECH absorption efficiency of ~ 90%. As a result of increased ion-electron coupling, the core ion temperature is expected to increase from the present value of ~50 eV to more than 150 eV, moving closer to a low collisionality regime. The radial electric field is calculated to be more negative in the core. The higher plasma density operation is expected to reduce the density of background neutrals. Because of the reduced flow damping due to neutrals, there should be higher flows in the direction of symmetry. The post-upgrade experimental program of HSX emphasizes areas that exploit these new capabilities: 1) exploring higher ion temperature and lower neutral density regimes, 2) optimizing the magnetic geometry to vary turbulent transport, 3) measuring plasma flows and electric fields at higher ion temperatures, more negative electric fields, and lower neutral damping and 4) measuring and understanding impurity transport. |
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NP11.00040: Experimental Study of Energy Confinement as a Function of Magnetic Well in HSX Henrique H Oliveira Miller, Michael J Gerard, John C Schmitt, Benedikt Geiger, Joseph N Talmadge, Colin Swee, Konstantin M Likin, Santhosh T Kumar, David T Anderson The Helically Symmetric eXperiment (HSX) is an optimized stellarator that has demonstrated excellent neoclassical transport properties [1]. However, strong anomalous electron heat fluxes have been observed in the outer plasma region (r/a $>$ 0.3), likely due to density gradient driven Trapped-Electron-Mode (TEM) turbulence [2]. This work explores how changing the magnetic field geometry between the standard configuration and a configuration with an enhanced magnetic well (Well configuration) affects energy transport and TEM-driven turbulence in HSX. The stored energy is compared between the two magnetic geometries. A power balance analysis with uncertainty propagation is carried out for both configurations to obtain experimental heat fluxes to compare with nonlinear GENE simulations. Previous results for the standard configuration of HSX suggest good agreement between GENE-simulated and experimental heat fluxes [3]. Moreover, GENE simulations for the Well configuration will be presented here. |
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NP11.00041: Core Electron Temperature Fluctuation Measurements via CECE in the HSX Stellarator Luquant Singh, Konstantin M Likin, Joseph N Talmadge, M.J. Pueschel, Benjamin Faber, Gavin W Held, David T Anderson A 16-channel radial correlation electron cyclotron emission (CECE) radiometer is used to study core (ρ < 0.5) electron temperature fluctuations in the Helically Symmetric Experiment (HSX) stellarator. Fluctuation amplitudes on the high field side and outside the region near the magnetic axis generally increase with increasing ECRH power. Near the magnetic axis (ρ < 0.1), fluctuation amplitudes are below the radiometer noise floor (δT/T < 0.1%), consistent with low gradient drive and dominant core neoclassical transport. An extended radial structure is identified in the high electron temperature gradient region for on-axis ECRH discharges. A comparison of temperature fluctuation amplitude and spectra from CECE with experimentally relevant nonlinear GENE simulations will be presented. |
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NP11.00042: Conceptual Design of a Heavy Ion Beam Probe for Studying Optimized Stellarator Physics in the Wendelstein 7-X Diane R Demers, Thomas P Crowley, Peter J Fimognari, Olaf Grulke, Humberto Trimino Mora, Ralph Laube Experimental measurements of characteristics in the plasma interior of Wendelstein 7-X (W7-X) are essential to increasing our understanding of optimized stellarator physics. The dynamics of particle and energy transport is an area of particular importance and, while much is inferred using power and particle balance estimates, a critical need for experimental assessment remains. A heavy ion beam probe (HIBP) can help fill this need and the design of one for W7-X is maturing, with substantial progress toward the critical milestone of a conceptual design review. The 2 MeV HIBP will acquire simultaneous, multipoint measurements of key quantities including the electric potential, and fluctuations of electron density and potential in the plasma interior. These will enable inference of the radial electric field, wavenumbers, and electrostatic fluctuation induced particle flux. We will present: anticipated measurement characteristics, predicted via simulations of beams through W7-X plasmas; status of the conceptual design, including CAD schematics of the system; characterization of key components such as the energy analyzer; an overview of project plans; and opportunities for collaboration. |
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NP11.00043: Realization of a Gas-Puff Imaging diagnostic on W7-X James L Terry, Adrian von Stechow, Seung-Gyou Baek, Sean B Ballinger, Carsten Killer, Olaf Grulke A Gas-Puff Imaging system designed to provide 2-d imaging of fluctuations on turbulence time-scales at the outboard edge of W7-X has been installed and is being commissioned for operation at the start of the next run campaign. The system will be used to study turbulence and filament dynamics in the SOL and in the magnetic islands, present as features of the island divertor configuration. Imaging of a ~78 x 38 mm region with 16 x 8 pixel resolution at ~1MHz framerates provides the capability to measure features with kperp in the range from ~0.04 to ~5 cm-1., with kperp ρs ~0.1.The system features high-throughput light collection by re-entrant optics imaging directly onto the camera, and a pop-up turning mirror that provides sight lines to the gas-puff region that are within ~10o of the local field lines. The novel gas-puffer features 2 vertically-stacked nozzles with “converging-diverging” cross-sections to provide improved collimation of the puffed gas. Because better collimation improves the spatial resolution and increases the chord brightnesses, careful measurements of the gas-puff cloud were made. An overview of the system, its expected capabilities, and the gas cloud measurements will be presented. |
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NP11.00044: The Development and Implementation of an Infrared Video Bolometer for the Edge Region of Wendelstein 7-X Aysia Demby, Felix Reimold, Oliver Schmitz, Glen A Wurden, Byron J Peterson, Gabriele Partesotti Direct measurements of the radiated power in the island divertor domain are key to understanding stable detachment and its link to plasma confinement in Wendelstein 7-X (W7-X). The Infrared Video Bolometer (IRVB) is an instrument used to measure radiation in plasmas, and has been successfully implemented at W7-X following the setups at LHD, JT-60U, and KSTAR. The commissioning and full application of this system will commence in the upcoming experimental campaign. This poster describes the development and set-up of the IRVB diagnostic observing the plasma edge region for W7-X. The system itself is described and compared to the traditional setup using resistive foil based detectors. Benefits of the IRVB, such as its high spatial resolution, are introduced. Spatial distortions affecting average temperature measurements in the setup at W7-X were evaluated, and a 2-D field of view was determined. With collected in-situ data, calibration was completed for increased temperature data reliability. These are the first steps to fully incorporate this new diagnostic. |
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NP11.00045: Beam emission spectroscopy diagnostic design and capabilities for two-dimensional turbulence measurement on Wendelstein 7-X Xiang Han, David R Smith, George McKee, Daniel J Den Hartog, Benedikt Geiger, Kurt Jaehnig, Christopher Seyfert, Thomas Gallenberger, Olaf Grulke, Thomas Windisch Turbulence transport is found to play a significant role in heat and particle confinements on Wendelstein 7-X (W7-X). A beam emission spectroscopy (BES) diagnostic is designed for studying 2D plasma turbulence dynamics at r/a∼0.5-1 by measuring the localized Doppler-shifted Balmer-alpha emission (n=3→2) from neutral heating beams on W7-X. We report the recent status of the diagnostic design, including optical assembly, detector platform, and the optical throughput. The field-aligned sightlines of BES is arranged to satisfy the constraints of the 3D magnetic topology and nearly radial heating beams while maintaining the sufficient Doppler shift to isolate the beam emission manifold on W7-X. The sightline grid with 1.4 cm spacing is evaluated to be sensitive to ion-scale turbulence with k⊥ρi≦0.4 at r/a=0.75 in the post-pellet regime of W7-X. We report on point spread function (PSF) calculations for a BES sightline grid in a variety of magnetic configurations and operational regimes of W7-X. Finally, the BES capabilities for 2D ion-scale turbulence measurements are summarized, the plan for in-situ calibration and experimental measurement on W7-X is foreseen. |
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NP11.00046: Localization Masks for Phase Contrast Imaging at Wendelstein 7-X Søren Kjer Hansen, Miklos Porkolab, Jan-Peter Bähner, Eric Edlund, Adrian von Stechow, Olaf Grulke
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NP11.00047: Continuous pellet fueling system for the W7-X stellarator Larry R BAYLOR, Steve Meitner An international team has developed and built a continuous, high-speed pellet injection system to fuel W7-X plasmas in quasi steady-state conditions. The team includes researchers from ORNL, IPP, PPPL and NIFS. This system will also serve as a prototype for the ITER pellet fueling system. The W7-X continuous pellet fueling system is designed to inject 3 mm H2 or D2 pellets into W7-X at speeds up to 1000 m/sec with a repetition rate of up to 10 Hz. A twin-screw extruder cooled by three cryocoolers is used to produce a continuous flowing ribbon of solid H2 or D2 that can be cut into a pellet and fired on demand by a light gas gun. The pellet size and repetition rate will be controllable in real-time to maintain optimum plasma profiles for confinement. The W7-X continuous pellet system has been assembled and commissioned at ORNL and is now undergoing commissioning at W7-X where it will be used in the next experimental campaign. High pellet reliability with H2 pellets was demonstrated as was the ability the adjust the speed from 200-1000 m/s and the pellet size from full to ½ the nominal 3 mm cylindrical size within a few seconds. Diagnostics to measure pellet mass, speed, and ablation emission have been implemented. |
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NP11.00048: HIGH ENERGY DENSITY Session Chairs: |
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NP11.00049: Variable magnetic field electron spectrometer used to measure Resonance absorption electrons in the range of 20-500 keV zeev Shpilman, Reed C Hollinger, Shoujun Wang, Ryan Nedbailo, Jaebum Park, Bedros B Afeyan, Jorge J Rocca Resonance absorption (RA) occurs when a p-polarized electromagnetic (EM) wave obliquely incident on a plasma density gradient tunnels past its turning point and resonantly excites an electron plasma wave at the critical surface. This phenomenon is important in several plasma physics experiments, for instance in inertial confinement fusion (ICF) where it has a deleterious effect. Direct measurement of these RA electrons in the energy range of few tens to a few hundred kev's is a complicated and challenging task, among other reasons due to the relatively low magnetic field needed. The solution described here is a magnetic electron spectrometer (ESPEC) with variable magnetic field, instead of the constant field that is usually applied in ESPEC designs. Applying a continually changing magnetic field, much lower magnetic field at the entrance of the ESPEC and a stronger one towards the end enables to measure a wide spectral range of electrons, between 20 keV to 500 keV. The current design was tested first in an EM- simulation and then by integrating the diagnostic device. The ESPEC energy scale was calibrated by placing a series of Aluminum filters in front of the image plate detector. The electron spectra were acquired from plasmas generated by irradiating Aluminum targets with the combination of: ~ 300 ps pulses followed by 2 ps duration pulse comprised of a series of 50-200 fs lasers pulses from the ALEPH laser at CSU. |
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NP11.00050: Zeeman Polarization Spectroscopy on Gas Puff Z-Pinches Jay S Angel, Euan Freeman, William M Potter, John B Greenly Zeeman Polarization Spectroscopy on 1 MA gas-puff z-pinches in CO2 and CO2 doped neon is being used to determine the magnetic field distribution in the |
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NP11.00051: Nonlocal Flat Optics for Z-Pinch Plasma Edge Detection Nicholas A Behrens Many high-energy-density (HED) physics measurements on laboratory plasmas involve identifying edges in object images, including measuring the radii of collapsing Z-pinch plasmas and following shadowgraphy or interferometry lines. Typically, edge tracing is performed though digital signal processing or by hand. However, recent developments in “nonlocal” (i.e., wavevector-sensitive) optics enable physical analog light processing, including edge enhancement, via designing a structure’s wavevector-dependent transfer function to act as a high-pass spatial-frequency filter for incident light. |
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NP11.00052: Rep-rated Technology Development at the General Atomics LAboratory for Developing Rep-rated Instrumentation and Experiments with Lasers (GALADRIEL) Gilbert W Collins, Mario J Manuel, Christopher McGuffey, Alicia Dautt-Silva, Devin Vollmer, Mike R Jaris, Brian Sammuli, Martin Margo The GALADRIEL facility is built around a commercial ~1 TW (<20 fs, 25mJ, 800nm) Ti:Sapph laser system capable of 10Hz operation and aims to address the needs of current and future High Energy Density (HED) facilities. Next-generation HED facilities utilize laser systems that are operable at rates of ~ 0.1 – 10 Hz, but often only field single-shot, or few-shot, diagnostics and target delivery systems. Because of this latter fact, significant development and testing of rep-rated diagnostics and target systems needs to occur for these facilities to achieve their true potential. GALADIREL will serve as a test platform for new rep-rated technologies, including the aforementioned diagnostics and target systems, as well as control feedback systems, data storage and management protocols, data processing, and machine learning techniques. Additionally, GALADRIEL is not intended only for use in the internal development of rep-rated technologies and processes at General Atomics, but as a user facility as well. Here we present updates, specs, and capabilities of the GALADRIEL facility as well as data from the initial commissioning experiments, which used the laser to generate ~MeV electrons via laser-wakefield characterized by a magnet-based spectrometer to measure the electron energy spectrum and a Shack-Hartmann wavefront sensor to measure areal electron density in the plasma. |
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NP11.00053: Influence of crystal thickness on reflectivity and energy resolution for transmission crystals Maylis m Dozieres, Christine M Krauland, Stanislav Stoupin, Jay Ayers, Nathaniel B Thompson, Jose E Castaneda, Tom McCarville, Joshua A Tabimina, Jeremy Huckins, Mai S Beach, John F Seely, Marilyn B Schneider The spectrometer calibration station (SCS) at Lawrence Livermore National Laboratory allows us to characterize and calibrate various crystals for different x-ray spectrometer geometries regularly used at the National Ignition Facility (NIF). Absolute throughput measurements are essential to properly diagnose the sources and extract meaningful results about the emitting plasma. Additionally, the SCS can help optimize instruments by testing different crystals. The Imaging and Spectroscopy Snout (ISS) is a NIF diagnostic that can be equipped with up to four different transmission crystals, each offering energy ranges from ~7.5 keV to ~12 keV with different energy resolutions. One critical parameter in such geometry is the crystal thickness. We present here an experimental study on the SCS comparing the integrated reflectivity and the spectral resolution measured for various unique ISS Quartz crystal thicknesses. The results will be discussed in the context of optimizing ISS measurements for ICF and will also be compared with theoretical calculations using pyTTE. |
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NP11.00054: Single-shot Dispersive X-ray Absorption Fine Structure Spectroscopy Using an X-pinch X-ray Source Jergus Strucka, Jack W Halliday, Ahmed T Elshafiey, Tatiana Shelkovenko, Sergei Pikuz, Simon N Bland The energy-dispersive x-ray absorption fine structure spectroscopy (EDXAFS) allows simultaneous measurement of density, ion temperature, and geometric structure of dense samples. Simultanously, the slope of an absorption edge allows the measurement of electronic temperature. These measurements are especially applicable to strongly coupled and optically opaque states of matter produced in laser-driven dynamic compression and x-ray radiatively driven experiments which are inaccessible to optical methods such as Thompson scattering. Dry Pinch I, a portable X-pinch developed at Imperial College, can produce on-sample photon flux of >10000 photons / eV around the Aluminium K edge within a single ~1 ns long x-ray burst. The X-pinch has a smooth and continuous spectrum enabling EDXAFS measurements. Using a spherical crystal, we measure a spectral bandwidth of 100 eV around the Aluminium K edge at 1559 eV (sufficient for near-edge structure measurements). As a proof-of-concept, we used the X-pinch to successfully measure the near-edge spectrum of a 2 micrometer thick aluminium foil in a single-shot mode. An experiment on the XP facility at Cornell will extend this measurement technique to higher energies, improve the integrated signal, and enable experiments with current heated samples. |
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NP11.00055: UPAC: A compact 96 channel 10GSa/s data recorder for HEDS applications Isar Mostafanezhad, Luca Macchiarulo, Ryan Pang, John Stahoviak, Marcus Luck, John L Porter, Quinn Looker We describe the design and characterization measurements for the UPAC-100: Ultrafast Pixel Array Camera. UPAC-100 is a compact 96-channel waveform digitizing data acquisition system with large buffer length (4096 samples per channel) and high timing performance (100ps sampling time, <10ps resolution), suitable for applications in HEDP and ICF diagnostics. It is designed to work with a variety of detector arrays such as high-speed photo-diodes and fast X-ray detectors. The system is being integrated with a silicon photomultplier (SiPM) and scintillator array to record single-hit neutron pulses for neutron time-of-flight (nTOF) spectroscopy. We have measured relevant UPAC-100 performance metrics such as bandwidth, linearity, power consumption, and trigger rate and will present how such specifications can enable new instruments or measurement techniques for fast imaging and nTOF diagnostics. |
Author not Attending |
NP11.00056: Bayesian Data Assimilation of Argon Gas Puff X-ray Source Data Collected on Sandia National Laboratories' Z-machine Marc-Andre Schaeuble, Patrick F Knapp, Jeffrey Fein, Taisuke Nagayama, Michael E Glinsky, Brandon T Klein, Kris Beckwith, Brent M Jones Argon gas puff implosions regularly produce > 300 kJ of ~ 3 keV photons on Sandia National Laboratories' Z-machine, making them one of the brightest laboratory x-ray sources in this energy range. Recent measurements have shown that only ~16 of the ~28 MA available on Z couple to the Ar gas puff. To better understand this high current loss phenomenon, Z gas puff plasmas are observed using several spectrometers, calorimeters, and photoconducting diamonds. Each of these diagnostics is analyzed separately and then combined to arrive at a final spectrum and x-ray yield, an important source performance metric. Unfortunately, this data analysis approach usually results in higher-than-desired x-ray yield uncertainties (~30%), which provides insufficient precision to resolve the high current loss problem. In this poster, we present a high-precision x-ray yield analysis using a Bayesian data assimilation approach for Ar gas puffs on Z. Advantages of this new approach include simultaneous and self-consistent analysis of all experimental data, more rigorous treatment of experimental uncertainties, an automated approach to excluding faulty diagnostics, and inherent diagnostic value-of-information testing capabilities. We present results using the Bayesian data assimilation approach to reproduce emitted spectra with an analytic model, as well as 1D, and 3D simulations. We also show initial application of our technique to Ar gas puff experimental data. Finally, we discuss the potential of the Bayesian assimilation to reduce experimental x-ray yield uncertainties to < 10%, which should enable us to progress in our understanding of poor current coupling in Ar gas puffs on Z. |
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NP11.00057: Developing experimental platform to benchmark x-ray fluorescence spectroscopy as a temperature diagnostic for high-energy-density plasmas Tanner Cordova, Edward V Marley, Michael Springstead, Richard A London, Howard A Scott, Tilo Doeppner, Farhat N Beg, David A Chin, Federica Coppari, James Emig, Stephanie B Hansen, Carolyn C Kuranz, Philip M Nilson, Philip A Sterne, Mike J MacDonald Accurate temperature models are critical in modeling planetary interiors and for inertial confinement fusion designs, as temperature affects many important physical properties such as ionization, heat transport, and compressibility. When constructing equation of state (EOS) models for high-energy-density plasmas, temperature measurements add an additional constraint to the more readily available pressure and density data. In this study we present the development of an experimental platform for x-ray fluorescence spectroscopy (XFS) at temperatures of 10s of eV to be used as a temperature diagnostic in EOS experiments. The experiments conducted at the OMEGA laser facility use a buried layer of copper tamped by plastic (CH) on both sides, the two sides are then irradiated by a symmetric laser drive. Simultaneous measurements using XFS and x-ray absorption spectroscopy yield independent measures of the temperature. These initial benchmark results from OMEGA are presented in the development of this x-ray fluorescence platform. |
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NP11.00058: Laser-Plasma Acceleration Driven Electron Radiography of High-Energy-Density Materials on the OMEGA EP Laser Gerrit Bruhaug, Hans Rinderknecht, Mingsheng Wei, Gilbert W Collins, J. Ryan Rygg, Jessica L Shaw, Matthew Freeman, Levi P Neukirch, Carl H Wilde, Frank Merrill Contact and projection electron radiography using a laser-plasma electron accelerator driven by the OMEGA EP laser are shown for static targets. Initial electron radiographs of laser-driven foils are shown along with a discussion of future experiments and applications for inertial confinement fusion, high-energy-density, and laser–plasma interaction experiments. A special emphasis is made on upcoming electron radiography experiments of hohlraum wall stand-in targets and the role electron radiography could play in determining sources of energy loss in hohlraums. |
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NP11.00059: Raman Spectroscopy Diagnostic Development for Dynamic Compression Experiments on OMEGA Alexa LaPierre, Arnold K Schwemmlein, Kevin Vencatasamy, Robert Boni, Gilbert W Collins, Ryan Rygg The pressures reached in dynamic compression experiments are sufficient to disrupt the electronic structure of matter, often inducing chemical and physical transitions. These dynamic processes are not directly measured by existing diagnostics that rely on a material’s ability to scatter x-rays. To this end, our work will develop a time-resolved Raman spectrometer for the OMEGA Laser System at the Laboratory for Laser Energetics. This diagnostic will measure the intensity and wavelength of a Raman-backscattered 532‑nm probe from laser-compressed materials. This diagnostic will directly probe the evolution of bond character of materials at high-energy-density conditions. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. |
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NP11.00060: Viscosity Measurements in CH at extreme conditions Afreen Syeda, Nitish Acharya, Danae Polsin, James Ryan Rygg, John J Ruby, Alex Chin, Hadley Pantell, Riccardo Betti, Gilbert W Collins, Arianna Gleason, Jessica Shang, Hussein Aluie Viscosity gives insight into the momentum transport in a system and plays a crucial role in mixing and growth of hydrodynamic instabilities. Viscosity measurements in High Energy Density (HED) states are particularly important to accurately develop hydrodynamic models and to bridge the gap between simulations and experimental results of complex systems such as Inertial Confinement Fusion. We measured viscosity in dynamically compressed epoxy (CH, 1.1 g/cc) by tracing the acceleration of particles embedded in the target. The OMEGA-60 laser facility was used to generate laser beams to drive a shock (peak⁓248 GPa) through the CH target, which was embedded with stainless steel (7.8 g/cc) or tungsten (19.3 g/cc) microspheres that were accelerated by the flow behind the shock. The particle positions were recorded with time-resolved X-ray radiography. The velocity of CH was calculated with the VISAR shock speed and the relation for polystyrene [1]. The velocities of the particles and CH were used to determine the viscous and inviscid force contributions acting on the particles using a shock-particle forcing model. From the viscous unsteady force, we determined the dynamic viscosity of shock compressed CH to be less than 10 Pa.sec. |
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NP11.00061: Optimization of Ti, Mn, Ni, and Cu Hybrid x-pinch X-ray emission in the 4-8keV photon energy range Nathaniel G Chalmers The Hybrid X-Pinch has been shown to be an excellent point source |
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NP11.00062: A New Proposed Target Area for Relativistic Laser–Plasma Experiments Using The Multi-Terawatt Optical Parametric Amplifier Line Laser System at the Laboratory for Laser Energetics Anthony Raymond, Jeremy Pigeon, Milton Shoup, Chad Mileham, Jake Bromage, Cheonha Jeon, Hans Rinderknecht, Dustin Froula The mid-scale Multi-Terawatt optical parametric amplifier line (MTW-OPAL) laser system is a multijoule, femtosecond-scale platform at the Laboratory for Laser Energetics. It was built to enable relativistic laser-plasma science and to inform the development of EP-OPAL, a planned kilojoule-femtosecond system within the Omega Laser Facility. A new laboratory area and target chamber are under development to accommodate experiments using the tightly focused MTW-OPAL beam. Irradiances reaching 1022 Wcm-2 using an f/2 off-axis paraboloid and deformable mirror are expected, with temporal contrast improvement via a double plasma mirror system. This will enable high repetition-rate investigations into relativistic laser-matter interactions, ultrafast laser science, laser and radiation diagnostic development, secondary source development, and advanced materials research. An overview of the laser capabilities, laboratory environment, and target chamber design will be presented along with descriptions of the first anticipated experiments to be conducted using this new resource. |
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NP11.00063: Development and Implementation of a Numerical Ray-tracing Laser Energy-Deposition Model for the PSC particle-in-cell (PIC) code Abdullah S Hyder, William R Fox, Derek B Schaeffer, Sophia Malko PSC, a particle-in-cell (PIC) code, is being used to directly simulate experiments involving high-energy-density (HED) plasma plumes. HED plasma plumes are formed in the laboratory by ablating solid-density targets with high-intensity lasers. Such laboratory experiments and their simulations are used for fundamental plasma studies. Currently, PSC uses an ad hoc plasma heating operator to represent the amount of energy a laboratory laser deposits as it propagates through a plasma. The ad hoc heating operator is derived from the plasma density profile found in DRACO, an independent radiation hydrodynamic simulation with a well-developed laser energy absorption model (W. Fox, et al, Phys. Plasmas 2018). To expand the scope of experiments that PSC can run and remove its dependency on DRACO, a new numerically calculated ray-tracing laser energy-deposition model was developed for PIC codes and implemented into PSC using existing theory on optical absorption by a plasma. The energy deposited per cell from the new model was benchmarked against and was found to be in excellent agreement with DRACO and analytical solutions for both shallow and highly oblique laser incidence angles. Additionally, energy is well-conserved by the new heating operator for large temporal domains. |
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NP11.00064: Particle-In-Cell Simulations of Ponderomotively Driven Plasma Waves with Improved Phase-Space Tiling David J Bernstein, Sean M Finnegan, Bedros B Afeyan, Luis Chacon The broad utility of the novel BARS/Mini-BARS [1] approach to improved phase-space tiling in particle-in-cell (PIC) simulations is considered through direct code-code comparison of simulations of ponderomotively-driven large-amplitude plasma waves, such as those found in laser-plasma-interactions in high-energy-density plasma experiments [2]. Long-time particle-trapping physics is explored, and simulations are 1D-1V with a short drive duration compared to the bounce period of trapped particles. Here, we assess both the computational speed-up and impact on preserving/improving resolution in dynamic regions of phase-space in PIC codes through the use of the Mini-BARS algorithm. Code comparisons are made between the fully-implicit kinetic plasma code DPIC [3], as well as a basic electrostatic PIC code written in Python and run on a laptop. |
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NP11.00065: Benchmarking the laser package in xRage against FLASH and experimental data John L Kline, Sean M Finnegan, Brian M Haines, Joshua P Sauppe This presentation will show comparisons of the Eulerian xRage code simulations for laser matter interactions to benchmark the accuracy of the code. The simulations results will be compared to experimental data collected using Thomson scattering. The results will include parametric studies to show degeneracy in the comparisons for interdependent variables in the code. In addition to comparisons with data, the results will be compared to the FLASH code another Eulerian code. Understanding the accuracy of the laser matter interactions is critical for a large number of High Energy Density Physics (HEDP) experiments which rely on these codes as design tools. |
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NP11.00066: SPECT3D Imagining and Spectral Analysis Code: Enhancements and New Capabilities Timothy Walton, Ming F Gu, Igor E Golovkin, Joseph MacFarlane SPECT3D is a collisional-radiative spectral analysis package used to compute detailed emission, absorption and X-Ray Thomson Scattering (XRTS) spectra, as well as filtered images, for multiple 1D, 2D, and 3D geometries. SPECT3D computes LTE and non-LTE populations using detailed atomic physics models. We present new improvements to SPECT3D, including improved radiation transport in 2D geometries, full implementation of atomic data produced by the Flexible Atomic Code (FAC), a new model for calculating Stark line widths, improvements and new features for XRTS, and general speed improvements. |
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NP11.00067: Computational investigation of shock-driven interface physics to study material viscosity at high pressures Sonya C Dick, Tyler Perez, Michael Wadas, Raymond F Smith, Peter M Celliers, Marius Millot, June K Wicks, Eric Johnsen An accurate understanding of viscosity trends and values of materials approaching the warm dense matter regime are poorly constrained and yet are important for diverse problems including mantle dynamics of super-Earths. Mantle dynamics drive a wide range of processes that shape terrestrial planets and the viscosity of a planet's mantle at relevant pressures (>100 GPa) is a critical transport property. This work focuses on constraining the viscosity of mantle-relevant materials at such pressures. We present a theoretical and computational framework to aid in experimental design and interpretation of results. We analyze the dynamic effects of a laser-generated shock traveling through a corrugated interface. Theory suggests that the evolution of the interface (i.e. the Richtmyer- Meshkov instability) and the decay of the transmitted shock is dependent on material viscosity. Using this theory, we present a method to obtain bounds on material viscosity. Simulations are performed to study the underlying dynamics using an in-house code. We improve our simulations with a stiffened equation of state to better represent the sound and shock speeds of the experimental materials. |
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NP11.00068: Discovering Physics and Improving Simulations using Neural Networks and Differentiable Kinetic Simulations Archis S Joglekar, Alexander G Thomas Modern libraries with implementations of Automatic Differentiation (AD) for machine learning can be used as general-purpose scientific computing libraries. We use two such libraries, JAX and PyTorch, to build differentiable kinetic plasma physics solvers i.e. solvers where each term and iteration in the solver is differentiable end-to-end. We leverage the ability to acquire fast and exact (to machine precision) gradients to 1/ discover novel physics using Vlasov-Fokker-Planck simulations and to 2/ develop improved numerical techniques for Particle-In-Cell modeling. In each, we judiciously place neural networks to learn functions which fulfill a holistic objective inline with the kinetic simulation. We also discuss the performance as well as the validation process for differentiable simulations. |
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NP11.00069: Identifying Governing ODEs in Irregular Physical Domain with Diffusion Gina R Vasey, Kristian Beckwith, Patrick F Knapp, William E Lewis, Brian W O'Shea, Andrew Christlieb, Ravi G Patel, Christopher A Jennings Simulating the complex plasmas created in experiments performed on the Z-Machine at Sandia National Laboratories is challenging due to both the range of spatio-temporal scales and the poorly constrained physical models needed to describe the system. In addition, the transient nature of the pulsed power drive results in a lack of a physically meaningful average or steady state about which the physical system could be linearized. Overall, this means that applying existing reduced order models (ROMs) to these transient, multi-scale, multi-physics systems presents a severe challenge. Here we develop a ROM for simulation data of 1D magnetic diffusion through a slab of finite resistivity. This problem addresses challenges regarding sharp boundaries and transient dynamics within the domain of interest. Making use of proper orthogonal decomposition (POD) coupled with the Sparse Identification of Nonlinear Dynamics (SINDy) model discovery method, we recover ordinary differential equations describing system evolution with varying amounts of problem periodicity. Finally, we examine the effects of noise and physics constraints when recovering this behavior. |
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NP11.00070: Diagnosing turbulent density fluctuations in Ne and Ar gas-puff Z-pinch implosions Alexander Rososhek, Eric S Lavine, Bruce R Kusse, William M Potter, David A Hammer Imploding Ne and Ar gas-puff Z-pinch plasmas on the 1 MA, 220 ns rise time COBRA pulser are studied with the primary focus being the turbulent non-thermal component of ion kinetic energy. Close to stagnation time, spectroscopic studies have shown that turbulence provides a physically sound picture,1 and accounting for variation in flow velocities yields better fitting results when analyzing Thomson scattering data.2 Additionally, recent research3 has demonstrated that this velocity distribution term is inconsistent with laminar velocity gradients and is likely indicative of turbulence. |
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NP11.00071: Scaling of pulsed power produced convergent shockwaves in insulators – kA to MA Simon N Bland, Jergus Strucka, Savva P Theocharous, David Yanuka, Yifan Yao, Jeremy P Chittenden, Luis Sebastian Caballero Bendixsen, Joshua Read, Cristian Dobranszki, Hugo W Doyle, Emilio Escauriza, Yakov Krasik, Daniel Maler, Alexander Rososhek, Sergey Efimov, Bratislav Lukic, Alexander Rack The pulsed power driven explosion of cylindrical arrays of wires in water has been used for the past decade to produce high speed, convergent shockwaves. On axis, the pressures that these shockwaves are expected to produce, which regularly stretch into the Mbar regime, should result in warm dense matter conditions being created, even with relatively small pulsed power drivers. Previously most experimental research has utilised drives with currents ~100-500kA, but this has recently expanded to include multi-mega ampere drives at one extreme, and currents as low as 30kA at the other. Coupled with either high resolution laser backlighting or the incredible multi-frame radiography capabilities of a 3rd generation synchrotron, we are now able to explore how the wire explosion technique scales with current, risetime and insulator material. Furthermore, new experiments have enabled the first imaging (by radiography) of the shockwaves created in spherical implosion geometries. This data will be used to plan a new campaign of experiments designed to create extreme pressures with the 8-10MA drive currents available on the M3 facility at First Light Fusion. |
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NP11.00072: Implementation of Non-Equilibrium Equation-of-State Model in Radiation-Hydrodynamics Code HELIOS-CR Igor E Golovkin, Joseph MacFarlane HELIOS-CR is a 1-D radiation-magnetohydrodynamics code that is used to simulate the dynamic evolution of plasmas created in high energy density physics (HEDP) experiments. Radiative and atomic processes in plasmas play a critical role in a wide variety of such experiments. We will discuss a new model that accounts for the effect that collisional-radiative atomic kinetics may play on the equation-of-state (EOS) and on overall plasma evolution. In the implementation of EOS models affected by collisional-radiative kinetics, we closely follow the formalism developed at LLNL (H.A. Scott, Chapter 4 in Modern Methods in Collisional-Radiative Modeling of Plasmas", Vol 90 (2016)). We will present the details of the newly developed model and discuss the simulation results for typical applications where the non-equilibrium atomic kinetics is expected to be important, e.g., for photoionized plasmas. |
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NP11.00073: Modeling Plasma Physics Phenomena with a Complex Multiphysics Code Alice Koniges, David C Eder Warm Dense Matter (WDM) is an emerging and challenging field at the crossroads of strongly and weakly coupled plasmas and solid, liquid and vapor states. We discuss a code and simulation capability, PISALE (Pacific Island Structured AMR with ALE), which has many unique features able to capture subtleties of the WDM regime and the processes involved in creating WDM states in laboratories. Multiphysics packages in PISALE include radiation hydrodynamics, surface tension, thermal diffusion, anisotropic material strength with material time history, advanced models for material fragmentation, and x-ray and ion beam deposition. The code framework is also used to model a variety of other phenomena including inertial fusion energy experiments, EUV lithography, hypersonic vehicle simulations, ground water flow, and droplet interactions. We give an overview of the code/framework and describe how it is being updated to study High Energy Density (HED) experiments at the Department of Energy's SLAC National Accelerator Laboratory. We also describe validation using previous IFE-relevant experiments at a variety of facilities including laser and ion-beam laboratories. The code is currently being used and improved by graduate students across the United States to study both high-performance computing techniques and simulations of these complex physical phenomena. It additionally serves as a teaching tool for the next generation of computational plasma physicists and we describe its educational use as well. |
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NP11.00074: Continuum Kinetic Studies of the Rayleigh-Taylor instability John Rodman, Bhuvana Srinivasan Rayleigh-Taylor (RT) instabilities are ubiquitous in plasma physics from astrophysical to laboratory regimes but are traditionally studied using fluid models. In this work, the continuum-kinetic capabilities of GKEYLL are used to simulate the RT instability in 2X2V (2 spatial and 2 velocity space dimensions) for a singly-ionized plasma in a regime where finite Larmor radius and nonlocal transport effects are relevant. Collisional effects have significant impact on the evolution of the instability, and comparisons are drawn between collisionless and collisional simulations at a variety of Knudsen numbers. |
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NP11.00075: Single-feature perturbation seeded Rayleigh-Taylor instability studied in planar geometry Camille Samulski, Bhuvana Srinivasan, Mario Manuel The Rayleigh-Taylor instability (RTI) has been identified as one of the largest inhibitors to high-gain inertial confinement fusion experiments. Thus, understanding RTI growth from single-feature perturbations, such as those caused by engineering features in capsules, and the potential damping effects of externally applied magnetic fields on instability growth is crucial. A National Laser User Facility (NLUF) experimental campaign has been developed to study single-feature perturbation seeded RTI studied on the Omega EP facility. The preliminary results from the first shot day of the experiment are presented. The simulation results focus on an unmagnetized shot configuration to observe the evolution of thin-layer theory RTI growth and validate platform performance. The effect of an externally applied magnetic field on the RTI growth and morphology will be investigated in the second shot day of the NLUF experimental campaign. The experimental configuration is simulated utilizing FLASH's HD capabilities. |
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NP11.00076: The Effect of Anode Shapes on Neutron Yield in a 4.4 kJ Dense Plasma Focus Device Veronica Eudave, Maria Pia Validivia, Swarvanu Ghosh, Jacquelynne Vaughan, Eric N Hahn, Fabio Conti, Farhat N Beg
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NP11.00077: Recent pulsed-power driven HED plasma experiments on the MAGPIE facility Sergey V Lebedev, Simon N Bland, Jack W Halliday, Stefano Merlini, Danny R Russell, Lee G Suttle, Vicente Valenzuela-Villaseca We present results from recent plasma experiments conducted at the MAGPIE pulsed-power generator (1.4 MA peak-current, 240 ns rise-time) [1]. These plasmas are characterized by long-lasting, multiply-ionized, supersonic flows (M~2-10) in the presence of strong magnetic fields (B~1-5 T), generated by the current drive, making them suitable for studying HED processes including shocks, reconnection, instability growth and radiative phenomena. |
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NP11.00078: Magnetized collisionless shock experiments on a pulsed power driven platform Lee G Suttle, Jack W Halliday, Stefano Merlini, Danny R Russell, Vicente Valenzuela-Villaseca, Sergey V Lebedev Collisionless shocks are frequently inferred in astrophysical systems where abrupt structural transitions occur over scales much shorter than mean Coulomb collisions. These transitions are instead mediated by a variety of wave-particle interactions with fields, leading to plasma instabilities across the shock transition. |
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NP11.00079: Global Eigenmode Analysis of The Filamentation Instability in a Dense Plasma Focus Justin R Angus, Steven F Chapman, Christopher M Cooper, Anthony J Link, Brian H Shaw, Andrea E Schmidt A dense plasma focus (DPF) is an open-ended coaxial plasma gun that terminates in a short-lived Z-pinch configuration on axis. DPFs operating with a deuterium fill produce a pulse of neutrons as the Z-pinch goes unstable. The neutron yield scales strongly with the pinch current. A poor breakdown/lift-off of the plasma along the insulator can lead to current restrikes, diverting current away from the pinch and decreasing the yield. The breakup of the plasma into filaments, which is a result of an electrothermal instability, has been observed in many experiments during the lift-off stage and is one possible source of poor lift-off. In this work, the filamentation instability during the lift-off stage of a DPF is studied using a global eigenmode description based on the extended-magnetohydrodynamic (EMHD) equations. This model incorporates the anode and insulator geometry into the analysis, which in some scenarios is found to have a large influence on the mode number and growth rate of the fastest growing modes. Results from 1D fully kinetic simulations of the lift-off are used as background conditions for the global eigenmode analysis. |
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NP11.00080: Pulsed-Power Driven Magnetic Reconnection within an Externally-Generated Field Thomas Varnish, Dylan K Robinson, George V Dowhan, Akash P Shah, Brendan J Sporer, Roman V. Shapovalov, Nicholas M Jordan, Raul F Melean, Ryan D McBride, Rishabh Datta, Jack D Hare We present results from the first experimental campaign to study pulsed-power driven magnetic reconnection in the presence of a strong magnetic guide field. On the MAIZE facility (450 kA, 240 ns rise time) we surrounded a dual exploding wire array load with an externally-powered Helmholtz coil to provide the guide field (0-2 T). A reconnection layer is formed from the interaction of oppositely-directed magnetic fields (~1-2 T) advected by carbon plasma flows moving at (~50 km/s). Line-integrated electron density measurements of the reconnection layer were made with spatially-resolved laser interferometry (1064 nm). The plasma dynamics were observed with both an optical fast-framing camera and a four-frame XUV MCP detector. B-dot probes were fielded to measure the advected magnetic field. Our results indicate that the external field significantly affects the dynamics of the inflowing plasma streams and reconnection layer produced, broadening the layer with increasing external field. At strong guide fields (2 T), we observe a void instead of a layer, suggesting the externally-applied field is frozen-out of the ablation flows and compressed until the incoming flows stagnate against the magnetic pressure. |
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NP11.00081: Novel studies of magnetized ions and electrons in shock-driven exploding pusher experiments Cody W Chang, Arijit Bose, Christopher A Walsh, Jonathan L Peebles, Vladimir Y Glebov, Patrick J Adrian, Graeme D Sutcliffe, Tucker E Evans, Maria Gatu-Johnson, Chikang Li, Fredrick H Seguin, Richard D Petrasso, Johan A Frenje We present an experimental investigation of how the implosion symmetry and dynamics of a laser-generated high-energy-density (HED) plasma is affected by a 25-50 T applied magnetic field. In this novel regime, both the ions (χi ~ 1) and electrons (χe >> 1) are magnetized, limiting their mobility perpendicular to the magnetic field because of their gyroradius rather than their mean free path. D3He gas-filled glass capsules were illuminated using a pole-heavy, 16.5 kJ, 1 ns laser pulse at OMEGA. 25 T and 50 T magnetic fields generated by the magneto-inertial fusion electrical discharge system (MIFEDS) were applied to these implosions. Time-resolved, spatially-resolved and integrated x-ray and nuclear measurements were made to study how magnetization affects electron-heat conduction in the plasma core and corona, kinetic ion physics, ion viscosity, and plasma instability and mix. Preliminary results suggest that the suppressed electron heat conduction causes a higher electron temperature (Te) and a steeper Te profile, and that the increased implosion asymmetry from the magnetic field increases the burn duration. Interpretation of the experiment is guided by 2D GORGON simulations. |
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NP11.00082: Generation of shocks between laser-produced plasma and jets emitted from conical wire array z-pinches. Luisa F Izquierdo, Felipe Veloso, Julio Valenzuela, Miguel Escalona, Diego Oportus, Mario Favre
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NP11.00083: Dynamic Structure Function in a Strongly Magnetized High Energy Density Plasma Scott D Baalrud, Louis Jose Strongly magnetized plasmas are characterized by having an electron gyroradius that is significantly smaller than the Debye length. This is a novel regime for plasma kinetic theory because electrons gyrate within the collision volume where interactions between particles take place. Recent work has developed new kinetic theories for strongly magnetized plasmas from linear response approaches as well as Boltzmann equation-based approaches. Here, we apply these recent advances to compute the dynamic structure function in a strongly magnetized plasma. We focus on the magnetohydrodynamic (MHD) regime. The model starts by developing generalized MHD equations for strongly magnetized plasmas. These have the same structure as standard MHD, but where the coefficients in the transport tensors are computed from a generalized collision operator of the new kinetic theory. These MHD equations are linearized and solved for the linear response function which provides the dynamic structure function in the hydrodynamic limit (long wavelength and low frequency). The predictions may be useful for interpreting scattering measurements in future magnetized HEDP experiments. |
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NP11.00084: Driven-Turbulence Simulations of High-Energy-Density Plasmas Abigail Armstrong, Adam Reyes, Yingchao Lu, Edward C Hansen, Eric G Blackman, Anaya Mohapatra, Petros Tzeferacos The magnitude of magnetic fields in the observable universe leads to questions regarding the physical processes that can grow and maintain them. One leading theory is fluctuation dynamo, which can amplify seed magnetic fields in a turbulent plasma to the point where the magnetic energy becomes an appreciable fraction of the available turbulent kinetic energy. Since the seminal numerical demonstration of fluctuation dynamo by Meneguzzi et al.,1 several numerical studies have pushed simulations codes and leveraged high-performance computing resources to explore fluctuation dynamo in magnetized turbulence at different regimes (for a recent review see Rincon2), although limited in the resistive magnetohydrodynamics (MHD) ansatz. Inspired by the recent experimental demonstrations of fluctuation dynamo by the turbulent dynamo (TDYNO)collaboration3,4 via laser-driven, high-energy-density (HED) experiments at the Omega Laser Facility at the University of Rochester's Laboratory for Laser Energetics, we present a series of 3-D FLASH simulations of driven turbulence that aim to study HED turbulence in regimes where plasma physics processes are important and extend beyond the one-temperature resistive-MHD ansatz broadly employed in existing theoretical and numerical models. The effort leverages FLASH's new extended MHD and HED physics capabilities and will furnish the theoretical foundations for future TDYNO experiments. |
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NP11.00085: Examination of the Coupling Between Electrothermal and Rayleigh-Taylor Instabilities in Pulsed Power Driven Implosions Matthew J Carrier, William A Farmer, Bhuvana Srinivasan Fast magnetohydrodynamic (MHD) instabilities dominate over slower m = 0 and m = 1 mode instabilities in high energy density (HED) pulsed-power settings when implosion timescales are faster than the Alfvén wave propagating through a material. For example, the electrothermal instability (ETI) is caused by the temperature and density dependence of electrical resistivity and results in temperature striations early in the current pulse. It is believed that this instability seeds the magneto-Rayleigh-Taylor (MRT) instability, which is known to cause non-linear mixing in inertial fusion concepts (ICF). The present work analyzes theoretical linearized growth rates for both the ETI and MRT, examines the coupling between the instabilities, and compares the results to single-mode 2D resistive magnetohydrodynamic simulations of Z-scale pulsed power configurations using a radiation-hydrodynamics code, Ares. |
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NP11.00086: Power Balance Studies Millimeter Wave and Infrared Radiometry Sydney Billingsley The behavior at stagnation of magnetized pinch plasmas, including gas puff Z-pinches, as well as X-pinches, is thought to be strongly influenced by the partition of energy during the early time implosion phase. In particular, the partition of energy in thermal, magnetic field, radiation, and turbulent kinetic energy channels may be of direct consequence to plasma performance at stagnation – e.g. in fusion and X-ray source applications. In order to further elucidate early time energy partition, a set of millimeter wave (mmW) and infrared (IR) radiometers have been fielded both on gas puff plasmas on the 1 MA COBRA generator at Cornell University, as well as on X-pinch plasmas on the ~ 100 kA LoboLTD generator at the University of New Mexico (UNM). The IR channels operate at 1100,1350, and 1550 nm, and the mmW channels are at 10, 94, and 119 GHz.. Comparisons will be made with the radiated power at early times during the pinch implosion between the X-pinch and Z-pinch systems under various operating parameters.The design of the radiometer channels, their calibration, and comparisons of results will be discussed. |
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NP11.00087: Electronic Stopping Power of Ions in Cold Targets and Warm Plasmas Thomas A Mehlhorn, Ming F Gu, Igor E Golovkin We report on a new wide range electronic stopping power model that builds on the random phase approximation (RPA) dielectric response formalism of Wang, et al and the local density approximation (LDA) with electronic density distributions calculated in an average atom model using the Flexible Atomic Code (FAC). The accuracy of this model has been greatly improved by implementing several extensions to RPA theory including a strong collision correction based on the binary collision theory of Zwicknagel for k>kmax, a static local field correction, an electron binding energy correction, and the Barkas effect. The combined corrections bring our RPA-LDA proton stopping power results in cold targets into close agreement with experiments across the periodic table (PSTAR database). We will also show results for the stopping of ions in warm dense plasmas as compared with the published data. We will describe our plans to implement this accurate ion stopping power model into an efficient and robust framework for computing ion energy deposition in HED plasmas spanning a wide range of temperatures and densities and to incorporate them into the HELIOS-CR hydro code (Prism) and Chicago (Voss), as well as an open-source standalone code. |
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NP11.00088: Measuring Transport Properties in Warm Dense Matter at the OMEGA Laser Facility* Travis Griffin, Cameron H Allen, Matthew Oliver, Laurent Divol, Otto L Landen, Andreas J Kemp, Yuan Ping, Markus O Schoelmerich, Wolfgang R Theobald, Tilo Doeppner, Thomas G White X-ray Fresnel Refractive - Diffractive Radiography (FDR), has been adapted to measure transient changes in density gradients between two species of warm dense matter (WDM). This platform combines micron-sized X-ray sources with isochorically heated cylindrical samples at large laser facilities such as OMEGA and NIF [1,2]. The high spatial coherence built into this technique enhances the refractive and diffractive features and provides a measurement of dynamic processes at the material interface [3]. We will discuss the successful imaging of thermal conductivity from recent OMEGA experiments and plans for implementation for upcoming experiments at NIF. |
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NP11.00089: Measurements of Temperature Evolution in Copper from Intense Proton Beam Energy Deposition Jacob Saret, Mathieu Bailly-Grandvaux, Christopher McGuffey, Joohwan Kim, Krish A Bhutwala, Philip M Nilson, T. Filkins, Wolfgang R Theobald, Alex Haid, Steven T Ivancic, Farhat N Beg Laser-driven intense proton beams provide short bunch duration and high rates of energy deposition optimal for laboratory studies in the Warm Dense Matter (WDM) regime. In the WDM regime, time-resolved X-ray spectroscopy can characterize samples during heating, yet this has largely remained unexplored in proton-heating experiments. We present an analysis of the first time-resolved Kα spectroscopy measurements from copper heated by an intense proton beam, using the High-Resolution streaked X-ray Spectrometer (HiResSpec) at OMEGA-EP. The EP short pulse laser (450-900 J, 5-10 ps) was focused onto a cone-enclosed partial hemisphere to generate and focus an intense proton beam onto a 10 μm- or 25 μm-thick solid copper sample. HiResSpec diagnoses the Cu kα1 and kα2 line emissions with a time resolution of a few picoseconds, allowing us to resolve temperature-dependent shifts of the lines; these correspond to sample temperatures up to ∼50 eV within ∼35 ps, according to atomic kinetics simulations. We compare these results to hybrid-PIC simulations and find consistent temperature evolution, when accounting for the temporal spreading of the proton beam as it traverses the cone. These measurements are an important contribution to the high-quality characterization required for benchmarking theoretical models in the WDM regime. |
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NP11.00090: An Analytic X-Ray Absorption Near-Edge Spectroscopy Model for Compressed Fe2O3 Matthew E Signor, David A Chin, Philip M Nilson, David T Bishel, Ethan Smith, Xuchen Gong, Mary Kate Ginnane, Brian Henderson, Danae Polsin, Suxing Hu, J. Ryan Rygg, Gilbert W Collins, John J Ruby, Amy L Coleman, Federica Coppari, Yuan Ping, Reetam Paul, Marion Harmand Understanding various electronic and magnetic changes at high pressures in Fe2O3 is not only an important solid-state physics question, but is crucial in describing Earth’s lower mantle. An x-ray absorption platform is being developed at the Laboratory for Laser Energetics to understand the electronic and crystal structure of compressed materials by simultaneously measuring x-ray absorption near edge spectroscopy (XANES) and extended x-ray absorption fine structure. Fe2O3 was quasi-ramp compressed up to 700 GPa and the pressure was determined using a velocity interferometry system for any reflector (VISAR) on the OMEGA-60 laser. An analytic method to extract the electronic occupation and temperature of the compressed sample from the XANES edge is being developed and compared to electronic structure calculations from ab initio molecular-dynamics simulations based on density function theory. |
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NP11.00091: Impact of wavefront helicity on electron plasma waves David R Blackman, John P Palastro, Jason F Myatt, Russell Follett, Alexey Arefiev The behavior of conventional electron plasma waves is relatively well-understood, but this understanding cannot be directly extended to plasma waves with helical wavefronts, i.e., those with azimuthal dependence. A challenge in studying helical plasma waves using kinetic simulations is that these waves must be driven to sufficient amplitude. One option is to drive the waves using laser beams as would be done in a high energy density experiment. This approach, however, is not well-suited for a focused study of helical plasma waves because of the feedback that can arise between the wave and the driving beams. We will present 3D PIC simulations that use an alternative approach in which plasma waves are driven by a low amplitude oscillating electric field with a specified helical structure. This setup enables us to study the fundamental properties of helical plasma waves in isolation, such as their evolution in the presence of wave-particle interactions. Preliminary results of the study will be presented. |
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NP11.00092: Effect of small normalized magnetic fields on rescatter of stimulated Raman scattering in the kinetic regime Roman Lee, Benjamin J Winjum, SJ Spencer, Mathieu Bailly-Grandvaux, Simon Bolanos, Mario Manuel, Frank S Tsung, Farhat N Beg, Warren B Mori We have previously shown [1] how backward stimulated Raman scattering (SRS) in the kinetic regime (kλDe ≈ 0.30 for backward SRS scattered plasma wave) can be mitigated by weak magnetic fields (ωc/ωp << 1) due to enhanced damping of non-linear electron plasma waves. In this presentation, we show results of 1D and 2D OSIRIS simulations of SRS in the kinetic regime for unmagnetized and magnetized plasmas at densities low enough (ne/nc < 11%) such that rescatter (backscattered light wave itself backscatters) is possible. We show that for these parameters, the magnetic field can enhance time averaged reflectivity of backward SRS by modifying plasma conditions and suppressing rescatter. Specifically, the magnetic field supresses rescatter by heating the plasma around the phase velocity of rescatter plasma waves, thereby increasing their damping and lowering the growth rate for rescatter. We present theoretical calculations which support this by indicating that these weak magnetic fields cause a transition of the rescatter instability from an undamped regime to a strongly damped regime. |
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NP11.00093: First STUD pulse experiments on controlling Resonantly excited electron plasma waves in high energy density plasmas. Ethan Welch, Kyle Jensen, Matthias Fuchs, Bedros B Afeyan, Jeffrey A Hittinger, Sean M Finnegan, John L Kline, Reed C Hollinger, Shoujun Wang, Jorge J Rocca Spike Trains of Uneven Duration and Delay (STUD pulses) are a promising means of controlling Laser Plasma Instabilities (LPI) by modulating the laser on the instability growth timescale. The nonlinear evolution of resonantly driven electron plasma waves involves disparate timescales: the plasma frequency, instability growth time, plasma wave walk-off time trapping time, wavebreaking time, and nonlinear self-organized phase-space-structure recurrence time. To optimize STUD pulses for LPI control, it is necessary to navigate between these various timescales. Using the high repetition rate, short pulse, petawatt laser system ALEPH at CSU, we have conducted the first STUD pulse optimization experiments of Resonance Absorption (RA) generated plasma waves and their control. 3358 shots were dedicated to the exploration of RA physics. We varied the angle between the 800 nm heater and interaction beams and their mutual delay, to change the density scalelength and plasma temperature. The amplitudes, durations, and delays between the 10 spike sequences were systematically varied and scattered spectra measured at 800, 400, 566, and 1600 nm. We will show the STUD pulse conditions that result in the largest stable plasma waves we could generate due to RA at nc and Stimulated Rahman Scattering (SRS) at nc /4. |
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NP11.00094: Field dependent line emission in magnetized plasmas Haritha K Hariharan, Roberto C Mancini, Peter Hakel, Vladimir V Ivanov The magnetic field effect on the atomic states and line emission of radiators in plasmas is a potential diagnostic tool for field measurements in laboratory and astrophysical plasmas. To model this effect, we calculate the magnetic field dependent eigenvalues and eigenstates in a non-perturbative fashion by diagonalizing the Hamiltonian with the magnetic field interaction. The result of this calculation produces field dependent atomic states that include the characteristic mixing of the magnetic field. Further, these atomic states can be used to calculate the line emission spectrum. The latter shows changes in the field free spectrum, including line intensities that are dependent on the magnetic field strength. We perform calculations for line emission in Neon-like iron ions and magnetic fields in the megagauss range for comparison with measurements in experiments driven by the 1 MA Zebra pulse power generator. |
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NP11.00095: Radiative Shocks and Instabilities in Colliding Supersonic Plasma Jets Stefano Merlini, Jack W Halliday, Lee G Suttle, Daniel R Russell, Vicente Valenzuela-Villaseca, Jeremy P Chittenden, Sergey V Lebedev Radiative shocks and transition to turbulence are active research frontiers in High Energy Density Plasmas for both astrophysical and Inertial Confinement Fusion applications. The structure of stagnation regions formed due to collision of supersonic plasma jets can be strongly affected by radiative cooling [2] and the presence of magnetic fields, leading to unstable shocks and turbulent plasmas. |
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NP11.00096: The electron cyclotron maser instability in laser ionized plasmas Thales Silva, Luis O Silva The electron cyclotron maser instability (ECMI) is a kinetic instability thought to be highly relevant to understanding radiation processes in a wide range of high-energy astrophysical phenomena. The ability to explore this instability in the laboratory can provide essential insights into astrophysics. However, generating plasmas with the required horseshoe or ring-like distribution functions in the laboratory can be highly challenging. Recent work [Zhang Sci. Adv., 2019] demonstrated that a circularly polarized laser that ionizes a neutral gas might generate ring-like distribution functions that quickly decay in other distributions. In this work, we use theory and particle-in-cell simulations (OSIRIS) to generalize previous studies in the presence of an external magnetic field, the condition relevant for the ECMI. We show that these rings in momentum stable have lower decay rates, and the plasma is unstable to the ECMI. We observe an excellent agreement between theory and simulations, not only for the growth rates but also for emitted radiation observed. Our proposed set-up opens a novel direction in laboratory astrophysics by enabling the observation of the maser radiation with the technology currently available in many laboratories worldwide. |
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NP11.00097: Collisionality studies of supersonic plasma jets on a 500 kA, 160 ns Linear Transformer Driver Kimberly Inzunza, Maria Pia Valdivia Leiva, Apsara M Williams, Samantha Fong, Fabio Conti, Farhat N Beg, Kimberly Inzunza Astrophysical objects such as Herbig-Haro and supernova remnants can produce supersonic plasma outflows. These objects can generate plasma jets through radiative cooling and collisionless shocks. To study plasma jet dynamics, experiments were conducted on CESZAR (Compact Experimental System for Z-pinch and Ablation Research), a >500 kA peak current and 160 ns rise-time Linear Transformer Driver (LTD). Counter-propagating supersonic plasma jets with varying degrees of collisionality were produced by driving two conical wire arrays of different materials; from carbon to tungsten. Collision rates and radiative cooling parameters were measured along with jet velocity and Mach number to investigate how collisionality impacts plasma jet formation. In agreement with previous results [1] obtained in a lower current LTD (GenASIS: 200 kA, 150 ns), it was found that plasma flows from low Z materials produce smooth, temporary stable collisional shocks and high Z materials produce strong, thin, and inconsistent short-lived collisionless shocks. These findings will inform scaling of future experiments to study jet dynamics in larger current systems. |
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NP11.00098: High-energy-density Targets Fabricated by The University of Michigan Sallee R Klein, Davis Gillespie, Kwyntero Kelso, Heath J LeFevre, R Paul Drake, Carolyn C Kuranz The University of Michigan has the distinctive capability of fabricating targets for a wide variety of high-energy-density physics experiments. |
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NP11.00099: Experimental results of pulsed-power-driven radial and rotating outflows to study accretion-driven stellar jets Hannah R Hasson, Marissa B Adams, Irem Nesli Erez, Matthew Evans, Imani Z West-Abdallah, James Young, Jay S Angel, Chiatai Chen, Euan Freeman, John B Greenly, David A Hammer, Bruce R Kusse, Eric S Lavine, William M Potter, Pierre-Alexandre Gourdain In this poster, we present recent data from several campaigns executed on Cornell's COBRA driver with the goal of studying the influence of magnetic field geometry and rotational velocity on the properties of the resultant bipolar outflow. For each campaign we focused on generating either purely radial-to-axial outflows or rotating "accretion-style" bipolar outflows. We used multiple designs of a 3D printed wire array holder to control the injection direction of the ablation stream from the wires, as well as the ratio of axial to azimuthal magnetic field. The properties of the outflows were characterized by temperature, velocity and density using interferometry, gated optical and ultraviolet imaging, and Thomson scattering diagnostics. We discuss the implications of these measurements and plans for future experimental campaigns. |
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NP11.00100: FLASH simulations that model laser-driven plasma experiments aiming to study second order Fermi acceleration at the GSI Helmholtz Centre for Heavy Ion Research Kasper Moczulski, Anthony Scopatz, Thomas Campbell, Charlotte A Palmer, Charles D Arrowsmith, Abel Blazevic, Dennis Schumacher, Martin Metternich, Haress Nazary, Paul Neumayer, Vincent Bagnoud, Oliver Karnbach, Christopher Spindloe, Archie F Bott, Subir Sarkar, Tony Bell, Alexander A Schekochihin, Robert Bingham, Scott Feister, Francesco Miniati, Don Q Lamb, Brian Reville, Gianluca Gregori, Petros Tzeferacos Non-thermal particles are common in the Universe and are observed in solar winds, supernova remnants, gamma ray bursts, and elsewhere. One of the methods used to explain how the particles are accelerated is the second order Fermi mechanism. While less efficient than diffusive shock acceleration, the ubiquitous nature of magnetized turbulence makes second order Fermi an important process. Magnetized turbulence can cause stochastic particle acceleration to non-thermal velocities, with the Hillas limit typically being used as the upper bound on such acceleration. With the combination of high-powered laser systems and particle accelerators it is possible to use magnetohydrodynamical scaling to understand this astrophysical phenomenon. We present FLASH MHD simulations used to interpret laser-driven plasma experiments that aim to reproduce second order Fermi acceleration at the GSI Helmholtz Centre for Heavy Ion Research. The experiments aim to demonstrate the second order Fermi acceleration process in stochastic magnetic fields. The simulations results are compared to the experimental measurements in an attempt to characterize the turbulent magnetized plasma responsible for the non-thermal particle acceleration. |
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NP11.00101: Modeling the Sedov Taylor Expansion of Core-Collapse Supernova in PERSEUS Imani Z West-Abdallah, James Young, Pierre-Alexandre Gourdain Magneto hydrodynamic (MHD) phenomena in astrophysics provide much of our current understanding of core-collapse supernovae remnants. Magnetically mediated spherical shocks, which appear as extremely thin discontinuities in the flow of ejected material, play a major role in these explosions and can be understood using an ideal MHD description. Under proper dimensionless scaling conditions, these astrophysical shocks may be recreated in a laboratory setting using pulsed power generators to create high energy density plasma via fast Z-pinch experiments. In this presentation, a radial foil Z-pinch configuration is simulated using PERSEUS (Plasma as an Extended-MHD Relaxation System using an Efficient Upwind Scheme) to reproduce a shock that has a radius that can be defined by the Sedov-Taylor similarity solution for spherical blast waves. Ion density, Reynolds number, Plasma beta, and Mach number were calculated to ensure shock formation and locate the boundaries of the shock radius. The results of the simulations show the radius of the blast wave to be in agreement with the r ~ t^(2/5) dependence found in the Sedov Taylor Solution. |
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NP11.00102: BEAMS: SHORT PULSE LASER PLASMAS Session Chairs: |
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NP11.00103: Construction and commissioning of the ZEUS laser system at the University of Michigan Anatoly M Maksimchuk, John Nees, Galina Kalinchenko, Bixue Hou, Yong Ma, Andrew McKelvey, Tan Shi, Paul T Campbell, Andre F Antoine, Mario Balcazar, Jason A Cardarelli, Nicholas Ernst, Rebecca Fitzgarrald, Colton Graham, Joshua Latham, Qian Qian, Igor Jovanovic, Carolyn C Kuranz, Alexander G Thomas, Louise Willingale, Karl M Krushelnick The Zettawatt-Equivalent Ultrashort pulse laser System (ZEUS) is being constructed at the University of Michigan as the National Science Foundation mid-scale user facility. The ZEUS facility includes a repetitive dual-beamline 3 PW laser system, a 100 J programmable shape multi-ns pulse driver, three radiation shielded experimental areas and will provide unique capabilities to explore nonlinear quantum electrodynamics, relativistic plasmas, particles acceleration, extreme laboratory astrophysics and nuclear photonics. Once completed, the ZEUS laser system will be the highest-power laser system in the US and will become a user facility for the US scientists and wider international research community. The construction status of the ZEUS facility including building renovation, laser, vacuum beam lines, experimental chambers, radiation shielding and the results of the initial commissioning experiment on the laser wakefield electron acceleration and radiation production at a 500 TW level will be reported. |
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NP11.00104: Zetawatt-Equivalent Ultra-short-pulse laser System (ZEUS) John Nees, Anatoly M Maksimchuk, Andrew McKelvey, Galina Kalinchenko, Bixue Hou, Paul T Campbell, Yong Ma, Nicholas Ernst, Igor Jovanovic, Carolyn C Kuranz, Louise Willingale, Alexander G Thomas, Karl M Krushelnick The National Science Foundation ZEUS facility is undergoing its preliminary sub-PW commissioning in 2022. With the renovation of 5,000sf of HEPA-filtered cleanroom space and 2500sf of radiation-shielded laboratory space delivered in 2021, the Zetawatt Equivalent Ultrashort laser construction pulse System (ZEUS) is now in progress. At the front-end of the laser chain, an Amplitude Lasers Pulsar incorporates double Chirped Pulse Amplification (CPA) with five stages of amplification, three programmable phase/amplitude devices, and CROSS-Polarization Wave (XPW) modulation for contrast enhancement, delivering 1.5 J pulses with demonstrated compression to 20fs. Pulses amplified in subsequent stages 1 and 2, pumped at ?20J and ?50J, respectively, are directed into a 500TW vacuum-based compressor. A vacuum-coupled chamber and external optical table support measurement devices for recording pulse duration, spectrum, spectral and temporal phase, wavefront, and temporal contrast. We will show the full configuration of the ZEUS laser and the results of measurements quantifying the laser performance as it is amplified through the first two out of what will ultimately be three amplifier stages. We will also show the roadmap to the completion of the system’s construction in 2023. |
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NP11.00105: Predictive Particle-in-Cell simulations for a near critical density ion acceleration experiment Thomas Kluge, Thomas Miethlinger, Ilja Göthel, Brian E Marrè, Long Yang A relativisticly intense laser can turn a near critical density plasma slowly transparent, facilitating a synchronized acceleration of ions at the moving relativistic critical density front. While idealized simulations promise extremely high ion energies in in this regime, the challenge resides in realistic assumptions for the laser and plasma parameters. Here we report on a numerical study including the preplasma expansion dynamics and realistic laser pedestal, the challenges in the near critical density regime, and the relevance for predictive capabilities of the simulations. |
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NP11.00106: BELLA iP2: The New High-Intensity Beamline at the BELLA PW Lieselotte Obst-Huebl, Kei Nakamura, Sahel Hakimi, Stepan Bulanov, Jared T De Chant, Cameron R Geddes, Anthony J Gonsalves, Axel Huebl, Zachary Kober, Tobias Ostermayr, Thomas Schenkel, Carl B Schroeder, Csaba Toth, Jeroen van Tilborg, Jean-Luc Vay, Eric H Esarey The new high-intensity iP2 beamline at the BELLA PW laser system enables frontier capabilities in High Energy Density Science (HEDS), including accessing exciting new regimes of ion acceleration. This system provides a focal spot of ~3 μm diameter, resulting in on-target peak intensities of > 5×1021 W/cm2. The high laser pulse repetition rate capability (up to 1 Hz), if paired with innovative, replenishable target systems, will increase the particle flux for applications and allows for the collection of large data sets, enabling adequate statistical analysis of the results. We foresee the implementation of a double plasma mirror to reach temporal contrast levels of 10-14 or lower on nanosecond timescales before the main pulse. These capabilities uniquely enable a series of scheduled experiments to study advanced ion acceleration mechanisms, investigate fundamental plasma processes relevant for Inertial Fusion Energy (IFE), and develop innovative plasma-based technologies with societal benefits, such as in radiation therapy. The iP2 beamline is accessible to users through LaserNetUS. |
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NP11.00107: Laser driven flash X-ray radiography of shocked materials David Broughton, Sasi Palaniyappan, Chengkun Huang, Nuno Candeias Lemos, Ann Junghans, Andy J Mackinnon, Arthur Pak, Prakash K Singh, Sallee R Klein, Thomas R Schmidt, Steven H Batha, Robert E Reinovsky, Andrea Favalli, Zhehui Wang, Bradley Wolfe Short-pulse laser driven x-ray radiography offers the potential to improve spatial and temporal resolution for imaging of shockwaves within materials. Previous studies have primarily used x-rays ⪅10 keV to image internal shockwaves or shock-induced fragmentation. Here x-rays in the tens to hundreds of keV are used to image a chromium foil with an internal shockwave of ~100 μm width and a factor of two increase in density. Performance of two experimental configurations was compared for both static and dynamic flash x-ray radiography at the OMEGA-EP facility. Experimental results are compared to synthetic radiographs generated using a combination of Particle-In-Cell and MCNP simulations and a ray-tracing program. Configuration one used a Ta cube target and displayed poor image quality due to presence of a dual x-ray source and high background. Configuration two had much better image quality using a Compound Parabolic Concentrator (CPC) cone with a Ta wire target to physically limit x-ray source, a magnetic field to deflect electrons, and a Cu casing to shield the sides and back of the image plate pack. By varying the short pulse beam delay driving the flash x-ray source spatial-temporal variations in shockwave dynamics (i.e., position, width, density profile) were resolved within the Cr foil, yielding results consistent with corresponding one-dimensional Helios hydrodynamic simulations. This supports extension of this technique to conduct shockwave diagnostics for cases less amenable to 1D modelling. |
Author not Attending |
NP11.00108: Characterization of laser-driven proton beams for static and dynamic radiography Thomas R Schmidt Jr, Steven H Batha, David P Broughton, Andrea Favalli, Elizabeth S Grace, Chengkun Huang, Metodi Iliev, Ann Junghans, Sasi Palaniyappan, Robert E Reinovsky, Raspberry A Simpson, Zhehui Wang, Bradley Wolfe, Benjamin Wyatt Laser-driven proton beams can be used as probes for static and dynamics radiography together |
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NP11.00109: Overview of the LANL Laser-Produced Multi-Probe Radiography Project Steven H Batha, David P Broughton, Chengkun Huang, Robert E Reinovsky, Thomas R Schmidt, Jeph Wang Future radiographic facilities for the US defense program will be required to provide more information as simulation codes improve in both physics’ fidelity and resolution. A possible approach is to use more types of probe beams in addition to, or instead of x rays generated by 20-MeV electron accelerators from a small number of directions. High power short-pulse laser systems can generate beams of protons, neutrons, and electrons, as well as x rays. The cost of these systems is falling rapidly, so it can be imagined that deploying multiple short-pulse lasers along with other, more traditional probes, will become feasible. In this project, we are following three paths to determine if such an approach will succeed for cm-scale objects. The first is an experimental one to determine if the presence of multiple short-pulse probes cause interference with each other, especially while radiographing dynamic objects. The second leg of this project is to determine if having multiple types of probes really does give more information on composition. Finally, an overall assessment of the viability of this approach will be made. Examples from recent experiments at the Omega EP laser will be presented. The initial approach to evaluating radiographs with multiple probes using the Bayesian Inference Engine (BIE) will also be given. |
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NP11.00110: Low divergence multi-10-MeV protons driven by a twisted driver Camilla Willim, Jorge Vieira, Victor Malka, Luis O Silva The study of compact high-intensity laser-driven proton sources is motivated due to a wide range of potential applications, from high brightness injectors for accelerators to inertial fusion and medical applications [1]. A crucial task to fully realize their potential is to reduce the proton bunch divergence while maintaining energy gain. |
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NP11.00111: Development of ultra-fast bright laser-driven x-ray probes with high intensity for Warm Dense Matter probing Katerina Falk, D C Gautier, Kirk A Flippo, David S Montgomery, Miguel A Santiago, Randall P Johnson, Tom Shimada, Xiayun Pan, Michal Smid, Viktoriia Zakharova, Lingen Huang, Nina Elkina Ultra-fast probing with x-ray sources for radiography and x-ray Thomson scattering is now of a great interest to plasma physics, in particular to study transport properties of WDM in relevance to astrophysical phenomena and inertial confinement fusion. Laser-driven K-alpha sources have proven to be excellent for this purpose, in particular for high energy laser experiments, however due to relatively low conversion efficiency in comparison to He-alpha and Ly-alpha sources, their applicability has been limited. Recent theoretical studies have shown that adding micro-scale structures to the laser-driven solid foils generating the x-rays can significantly enhance the flux of such sources. So far, only a handful of experimental studies of the use of these micro-structured targets has been carried out. We present experimental results developing bright x-ray sources driven by short-pulse lasers with copper foam targets. We have used low density copper nanowire foams driven by the Trident laser at ~1020 W/cm2 and 80 J energy. X-ray spectroscopy methods were used to characterize the laser-target interaction exploring the absorption efficiency of the laser and subsequent effect on the production of hot electrons and strongly enhanced target heating compared to flat foils. The experimental results were compared with atomic and particle-in-cell simulations. |
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NP11.00112: Developing Predictive Modeling of Laser-Plasma Interactions for X-ray Radiographic Imaging Scott V Luedtke, A Favali, Chengkun Huang, Mark J Schmitt, Alexander Seaton, Avneet Sood, David Stark, Lin Yin, Joshua E Coleman, Donald C Gautier, Christopher E Hamilton, james hunter, Benjamin J Jones, Marc Klasky, Albert J Mendez, Sasikumar Palaniyappan, Joseph Strehlow, Christopher Tomkins, Brian J Albright Novel MeV x-ray sources based on high-power short-pulse lasers have the potential to revolutionize radiography with their small spot size, short pulse duration, low cost, and flexibility. In this poster, we report on multiphysics modeling of experiments to produce MeV x-rays. Our goal is to develop a predictive simulation capability to aid in the development of x-ray radiographic technologies. Using particle-in-cell and Monte-Carlo particle-transport codes, we simulate electron acceleration in short-pulse laser experiments with a variety of targets and calculate photon spectra resulting from bremsstrahlung radiation in a high-Z converter. We find that common figures of merit (e.g. laser absorption fraction) may not directly translate to desired experimental outputs (MeV x-rays). We discuss challenges of performing predictive simulations and ways to address those challenges. |
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NP11.00113: MeV x-rays from Petawatt laser interaction with flat, foam, and nanostructured targets Joseph Strehlow, Alemayahu Bogale, Sandra Bruce, Hui Chen, Joshua E Coleman, Todd Ditmire, Juan C Fernandez, Rebecca J Fitzgarrald, Donald C Gautier, Chengkun Huang, Christopher E Hamilton, james hunter, Benjamin J Jones, Scott V Luedtke, Eli Medina, La Moyne T Mix, Sasi Palaniyappan, Hernan J Quevedo, Mark J Schmitt, Alexander Seaton, Avneet Sood, Michael M Spinks, David Stark, Chris Tomkins, Justin Twardowski, Ashlyn Van Pelt, Lin Yin, Brian J Albright The interaction of an intense laser with overdense targets can readily generate MeV electrons, which in turn can be converted into MeV x-rays via the Bremsstrahlung process. With their ultrashort duration (~ps) and high resolution (<100 µm), such energetic x-rays have a wide variety of applications in both the dynamic and static radiography of dense materials. Here we report on results from the Texas Petawatt laser (120 J, 140 fs, ~5×1020 W/cm2) to study the production of secondary radiation from thin (~µm) targets, which is subsequently injected into thick (~mm) targets. Multi-stage numerical modeling is required for good agreement, with particle-in-cell modeling predicting the electron acceleration, followed by Monte Carlo methods to simulate the conversion of MeV electrons into MeV x-rays. Experiment and simulations indicate that padding the mm-thick targets with critical density foam or nanostructures provides an avenue to brighter MeV x-ray beams, while showing that even high laser contrasts (>109) must be accounted for. |
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NP11.00114: Development of laser-based MeV sources for static and dynamic radiography Brian J Albright, Sasikumar Palaniyappan, james hunter, Lin Yin, Alemayahu Bogale, Joshua E Coleman, juan c fernandez, Rebecca Fitzgarrald, Donald C Gautier, Chris E Hamilton, Chengkun Huang, Benjamin J Jones, Marc Klasky, Scott V Luedtke, Mark J Schmitt, Avneet Sood, David J Stark, Joseph Strehlow, Christopher Tomkins, Justin Twardowski MeV x-ray sources based on high-power short-pulse lasers offer several advantages over conventional pulsed-power sources, including small spot size, flexible configuration, and tailorable spectra. This paper will report on results from a new LANL effort to develop flexible, compact x-ray sources for static tomographic radiography as well as dynamic multi-axis radiography at facilities requiring high brightness dynamic imaging. The goal is to develop sources with high resolution, short pulse duration, and tunability in dose and spectrum. Results from a laser/target optimization study using the VPIC kinetic plasma modeling code and the MCNP transport code will be reported. Results from recent experimental campaigns will also be presented. |
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NP11.00115: Simulation of laser preplasma interaction with ionization dynamics Chengkun Huang, Brian J Albright, Alemayahu Bogale, Joshua E Coleman, Andrea Favalli, Juan C Fernandez, Rebecca J Fitzgarrald, Donald C Gautier, Chris E Hamilton, james hunter, Benjamin J Jones, Marc Klasky, Scott V Luedtke, Albert J Mendez, Sasi Palaniyappan, Mark J Schmitt, Alexander Seaton, David Stark, Joseph Strehlow, Christopher Tomkins, Justin Twardowski, Lin Yin Performance of laser-driven particle/radiation sources from solid targets is often impacted by the interaction of the laser with the preplasma generated by laser pedestal. The preplasma is usually ionized to a low charge state by the laser pedestal but it can be further ionized by the arrival of the main pulse, creating a different preplasma condition. We conducted particle-in-cell study of the effect of ionization dynamics in the preplasma using initial conditions from well-defined density profiles as well as those from the rad-hydro simulations of the pedestal target interaction. Spectrum and yield of the hot electrons generated are compared with the simulations assuming fixed charge state without ionization. The dynamics of the ionized electrons in the interaction is analyzed and will be discussed in the context of experiments aiming to optimize X-ray photon production. |
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NP11.00116: Filamentation compression of CPA laser pulses and beam applications Jon M Murphy, Milos Burger, Nicholas J Peskosky, John Nees, Karl M Krushelnick Compression of amplified laser pulses beyond the limits of a compressor grating-setup has been a fruitful topic of research for decades. Filamentation compression offers a solution which benefits from a higher energy capacity and being easier to couple light into than the the hollow-core fiber compression scheme. Here, 40 fs CPA laser pulses with 40 nm FWHM bandwidth are spectrally-broadened and compressed. An experimental analysis of the post-filamented beam's spatial profile, spectrum, and pulse length is presented. Also included is an analysis of various appropriate applications for this beam and ideally how its performance compares to the pre-filamented beam in a few laser-plasma interaction experiments including Kα x-ray generation and LWFA. |
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NP11.00117: High Repetition Rate, High Intensity Vector Beams at Short Wave Infrared Wavelengths Danny W Attiyah, Hunter G Allison, Christopher Gardner, Peter Kazansky, David D Schmidt, Charles G Durfee, Franklin J Dollar
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NP11.00118: Relativistic Four Wave Interactions Enabled Through Nonlinear Resonance Conditions Alec Griffith, Kenan Qu, Nathaniel Fisch Four wave interactions at mildly relativistic intensities could be harnessed to generate high energy and high frequency laser pulses [1]. Four wave interactions are additionally complicated by relativistic self- and cross-beam phase modulation. Depending on the context, phase modulation may restrict [2] or widen [3,4] the viable parameter regime for efficient energy conversion. We further analytically and numerically explore how the combination of these two relativistic processes could be manipulated to create unique amplification regimes. |
Author not Attending |
NP11.00119: Chirped Pulse Compression in Plasma Min Sup Hur, Hyyong Suk CPA technique has made available multi-petawatt laser pulses. However, millions times stronger lasers are required to experimentally verify the prediction of modern theoretical physics, e.g. pair-production or radiation reaction. As it is obvious that the conventional CPA cannot be directly scaled-up due to the compression gratings, fundamentally different approach should be taken. While diverse novel ideas are investigated for this goal, such as Raman backward amplification, Brillouin scatter, or plasma gratings, here we present a new idea that is completely different from previous ones. In our new system, we exploit the plasma-intrinsic, density-dependent refractive index. From PIC simulations, we obtained almost 100% compression of an 2.5-ps incident pulse into 10 fs. Theoretical estimation of various instabilities shows that they can be suppressed well not to affect the compression process deletoriously. We discuss the potential of our new idea as a next generation post-CPA. |
Author not Attending |
NP11.00120: Breaking the Radiation Frequency Limit in PIC Codes Miguel Pardal, Ricardo A Fonseca, Jorge Vieira Radiation emission plasmas is often a result of collective effects associated with the dynamics of relativistic charged particles. A common numerical approach to model their motion involves the Particle-In-Cell scheme which solves the full set of Maxwell's equations and the relativistic Lorentz force for the charged particles. The recently developed Radiation Diagnostic for OSIRIS (RaDiO) can retrieve the emitted spatiotemporal electromagnetic field structure of the emitted radiation in OSIRIS simulations, even at wavelengths smaller than the PIC resolution, by relying on the Liénard-Wiechert Potentials. OSIRIS can run with a high level of efficiency in most of the largest CPU-based supercomputers. Nevertheless, in recent years, GPU accelerator boards have been employed in supercomputers to the point where some of the most powerful machines nowadays are GPU-based systems. In these architectures, the CPU nodes are equipped with additional GPU boards that can be used to perform highly parallelizable computations such as obtaining the emitted radiation in a PIC code. This work describes the implementation of the radiation algorithm in the GPU architecture and its integration into OSIRIS. Several performance benchmarks confirm the efficiency and applicability of this diagnostic. |
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NP11.00121: Development of a short pulse neutron source using the NIF-ARC laser Jackson G Williams, Shaun M Kerr, Graeme G Scott, Kelly D Hahn, Maurice B Aufderheide, Joseph Bendahan, Blagoje Z Djordjevic, Clement S Goyon, Matthew P Hill, Andreas J Kemp, Joshua Ludwig, Tammy Ma, Andy J Mackinnon, Derek A Mariscal, Matthew M McMahon, Dean Rusby, Matthew P Selwood, David J Schlossberg, Raspberry A Simpson, Franziska Treffert, Scott Wilks, Ghassan Zeraouli Neutron sources are used in a wide variety of applications including material science, isotope production and radiography. Short pulse laser-driven neutrons have unique characteristics such as sub-ns durations and high peak brilliance. The peak flux that is often required to probe temporally evolving environments has not yet been demonstrated for these laser-driven sources. Here, we report on the platform development of a pitcher-catcher neutron source using the large spot size, multi-kJ, multi-picosecond NIF-ARC laser. The initial experiments explored laser energy scaling at ARC conditions and catcher configuration and measured neutron yield, spectrum, and directionality. |
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NP11.00122: The formation time of a photon is equal to 3/4 of the wavelength divided by the speed of light Han y yong Quan The precursors of photons exist within atoms or between different atoms, and they are meta-charges that revolve around each other, and the mass of meta-charges is variable. Photons are formed when the mass of the photon precursor is lost to half of its original mass. The mass of the photon precursor is m, and its connotative energy is: mc2. When the mass loses m/2, the energy formed is: mc2/2. According to the law of conservation of energy, the energy of the remaining mass of the photon precursor must also be accelerated to: mc2/ 2. I summarize the equation: M2R=Q, where M is the mass of the photon, R is the space of the photon, and Q is a constant. In fact, 2R is the wavelength of the photon propagation. The diameter of the extrapolated photon is 4 times that of the photon's predecessor. That is, 3/4 of the wavelength at which the photon travels at the speed of light should be increased by the formation of photons. |
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NP11.00123: Electron and Photon spectra in Strong Field QED Scattering Experiments Óscar L Amaro, Marija Vranic Scattering electron beam with peta-watt optical lasers is planned for experiments in current and near-future laser facilities. Most analytical models associated with the evolution of the electron distribution function, expected photon emission and pair creation have been developed assuming the laser is a plane wave with a temporal envelope. This approximation is valid for a perfectly synchronized collision (in space and time) where the laser waist is large compared to the electron beam size. In an experiment, not all electrons will interact with the same peak laser field and the laser Poynting instability makes it difficult to ensure the spatial synchronization on all shots. To take this into account, it is possible to estimate the effective laser intensity of interaction for each particle and generalize the scaling laws previously derived to more realistic geometries including 3D effects. Recently, we have shown that the positron yield in focused laser-electron scattering can indeed be estimated using this strategy, where we have derived an analytical description for the effective intensity distribution function [1]. In this work, we developed a semi-analytical model for obtaining the final electron distribution function using both classical and quantum radiation reaction descriptions, and including several non-ideal features such as offset from the laser focus, interaction at an angle (in particular at 90º), non-monoenergetic beams, beam divergence, and tight-focusing. We've compiled these results into a light, parallel, user-friendly open-source toolkit, that can give real-time support for the upcoming laser experiments. |
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NP11.00124: Compression of Multi-millijoule short pulse Lasers in plasma Christopher Gardner
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NP11.00125: Fundamental research of laser wakefield acceleration driven by TW-class laser Takamitsu P Otsuka, Takahiro Gunji, Kouichi Iida, Rui Takahashi, Daiki Nishida, Duthika Perera, Kosuke Kataya, Yuta Ikoma, Noboru Yugami Laser wakefield acceleration (LWFA) driven by low peak power laser system have been investigated. In this case, relatively longer laser pulse is employed for creating plasma compared to standard LWFA. The plasma wavelength and the pulse length of laser not equal, thus, wakefield not grow up resonantly. |
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NP11.00126: Towards the observation of linear Breit-Wheeler process in ultra-intense laser-plasma experiments Yutong He, Thomas G Blackburn, Toma Toncian, Alexey Arefiev Linear Breit-Wheeler (BW) process (γγ→e+e-) is one of the fundamental processes in the theory of quantum electrodynamics, but yet to be observed in experiments. Previous research [Comm. Phys. 4, 139 (2021)] has shown that a significant number (>108) of linear BW pairs can be generated by colliding two ultra-intense laser pulses (at intensities of 2×1022 W/cm2) inside a plasma channel. Simulations with our newly implemented module demonstrate that these positrons can be accelerated to GeV energies by the remaining laser pulses and form collimated energetic linear BW positron beams. The impact of target parameters on the pair yields by different pair creation mechanisms in the system is also investigated. It is found that the relative contributions to the pair yields by the linear BW, the nonlinear BW, and the Bethe-Heitler processes can be controlled by only changing the target length and channel density within the experimentally controllable regime [Phys. Plasmas 29, 053105 (2022)]. Our result shows that the setup of colliding pulses inside a structured plasma target has the potential to achieve the first observation of the linear BW process using real photons with experimentally available laser pulses and targets. |
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NP11.00127: HED: SHORT PULSE LASER PLASMA Session Chairs: |
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NP11.00128: Electron density, temperature, and axial charge displacement of an ultrashort pulsed laser plasma filament inferred from electrical conductivity measurements based on strong field approximation Edward L Ruden, Jennifer A Elle The ionization rate and most probable momentum vector of electrons upon ionization and after optical pulse passage vs. ionization time t₀ is found from a nonadiabatic strong field approximation. The resulting electron temperature T after thermalization, axial current density J, and number density n are found as functions of electric field peak E0. Conductivity σ as a function of E0 is then found from its dependence on n and T. Inverting results in E0 and, therefore, n and T as functions of σ. These are used to determine n and T of a linearly polarized USPL pulse's trailing plasma filament in air at a range of pressures from previously reported measurements of its σ and radial density profile. The measurements are based on the attenuation of a 3.2 GHz TE10 mode externally driven in an S-band waveguide across which the filament passes in the TE direction through holes, and fast framing camera images, respectively. The diagnostic also measures the axial charge displacement Q (current time integral) from the signal when the 3.2 GHz driver is turned off. To help validate the model, Q is independently estimated from the product of its J result, the measured filament's cross-sectional area, and a current decay time estimate. |
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NP11.00129: Measurement and analysis of K-shell emission spectra of Si nanowire arrays irradiated at relativistic intensities Jang Hyeob Sohn, Gyeongbo Kang, Gyusang Lee, Changhoo Lee, Min Sang Cho, Ahhyun Seong, Byoung-ick Cho Relativistic laser-matter interaction has been an important platform for studying the extreme properties of high-energy-density(HED) plasmas [1]. Recently, nanowire array targets have attracted much interest due to their high optical absorption [2]. They are considered a unique means of efficient x-ray source development and accessing the well-defined HED regime [3,4]. Here we present the measurement and analysis of K-shell emission spectra (1.70-2.04 keV) of Si nanowire arrays irradiated by 150 TW Ti:sapphire laser pulses at the CoReLS. A peak laser intensity is above 1020 W/cm2. Ly-a, He-a, and their satellites emissions are measured for various nanowire lengths and laser pre-pulse conditions. We also calculate Si K-shell emission spectra using a collisional radiative code FLYCHK [5] for various plasma parameters. Detailed modeling and comparison with experimental data will be presented. |
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NP11.00130: Leveraging high temporal and spectral resolution to study solid-density plasma ablation Brooklyn Frances Kraus, Lan Gao, Kenneth W Hill, Manfred L Bitter, Philip C Efthimion, Reed C Hollinger, Shoujun Wang, Huanyu Song, Ryan Nedbailo, Jorge J Rocca, Roberto C Mancini, Cuyler B Beatty, Michael J MacDonald, Ronnie L Shepherd X-ray emission spectroscopy is a key diagnostic for laser-produced plasmas, especially at high densities where most optical- and particle-based measurement techniques cannot probe. We investigate plasma phenomena near solid densities by pairing an ultrafast streak camera (temporal resolution Δt < 1 ps) with focusing quartz crystal spectrometers (spectral resolving power E/ΔE ~ 104) to capture the evolution of emitted x-ray line shapes. Since line shapes encode plasma properties such as densities, temperatures, and flows, the measurements access new information about high-density plasma physics. One application of this capability is the study of solid material ablation by relativistic laser pulses (intensity > 1021 W/cm2). Streaked x-ray spectra emitted from discrete layers of highly ionized tracer material contain unshifted x-ray line transitions at early times, representative of hot, non-flowing plasma. Later in time, the same line shapes develop Doppler-shifted components, indicating time-evolving ion flows as plasma ablates into vacuum. This data can quantify a nonzero and depth-dependent time delay between laser-induced plasma heating and the initiation of expansion. |
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NP11.00131: On Possibility of Magnetic Monopoles Generated in Decaying Colossal (1016T) Magnetic Fields in Femtosecond Laser—Pb-Pellet Interaction. V. Alexander Stefan A novel idea is proposed: the magnetic monopoles [1] [2](a few gD, Dirac magnetic charge) might be generated via the laser-matter interaction physics.[3] A femtosecond laser (≥ 10MJ; ≤ 0.1μ [4]) in interaction with a Pb-pellet (diameter ≤100 μ) might produce, it seems to me, the B-fields of the threshold-decay-intensity, so as to spontaneously decay into Dirac-anti Dirac monopoles. [1] P.A.M Dirac, Proc. R. Soc A133, 60, (1931).
[2] J.D. Jackson, The Nature of Intrinsic Magnetic Dipole Moments, in V. Stefan, Editor: Physics and Society--Essays in Honor of V.F. Weisskopf by the International Community of Physicists, (Springer-Verlag, New York, 1998); pp.129-152; Physics Today, April, 2022; pp.14-16.
[3] V. Alexander Stefan: Laser Fusion Research: Generation of Suprathermal Particles, Laser Radiation Harmonics, and d. c. Magnetic Fields. Final Report-1989. Institute for Advanced Physics Studies, Stefan University, La Jolla, CA, USA[NTIS: https://www.osti.gov/biblio/5309387]
[4] V. Stefan, D.E.Parks, M.Rotenberg, E.R.Waisman, A.R. Wilson: Bull.Am.Phys.Soc. 32,No.9,1713 (1987); Ultra short-wavelength beat-wave-driven FEL
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NP11.00132: Electron-positron pair production by linear Breit-Wheeler process in ultra-short petawatt laser-plasma interaction Kaoru Sugimoto, Natsumi Iwata, Takayoshi Sano, Yasuhiko Sentoku In this work, we have demonstrated with a help of particle-in-cell simulations that an ultra-short petawatt laser light self-organizes a photon collider in a near critical over-dense plasma and produces a large number of positrons via the linear Breit-Wheeler (BW) process. An ultra- intense laser pulse propagates in an over dense plasma by its relativistic transparency with forming a magnetic channel structure and accumulating electrons in front of the pulse. In the magnetic channel, the laser light drives relativistic electrons and induces collimated gamma-ray photons via synchrotron radiation. While at the pulse front electrons are accelerated backward with relativistic energies by an electrostatic field induced by the electron accumulation. The relativistic electrons moving backward emit photons when they collide the laser pulse. These photons collide with the gamma-ray photons and induce electron-positron pairs via the BW process. We also found that the generated positrons are accelerated by the electrostatic field to GeV energy with a narrow divergence of ±10 degrees. In the talk, we'll report the physics of the collider formation and details of the simulation results. |
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NP11.00133: Energy enhancement of laser-driven ions by radiation reaction and Breit-Wheeler pair production in the ultra-relativistic Breakout-Afterburner regime Shikha Bhadoria, Mattias Marklund, Christoph H Keitel The impact of radiation reaction and Breit-Wheeler pair production on acceleration of fully ionized Carbon ions driven by an intense linearly-polarised laser pulse has been investigated in the ultra-relativistic Breakout-Afterburner (BOA) transparency regime [1]. Against initial expectations radiation reaction at ultra-high laser intensities is found to enhance the energy gained by the ions. The electrons lose most of their transverse momentum and the additionally produced pair plasma of Breit-Wheeler electrons and positrons co-stream in the forward direction.This leads to changes in the phase velocity of the Buneman instability, that is known to aid ion acceleration in the BOA regime, by tapping the free energy in the relative electron and ion streams [2]. We show that this can further improve the highest Carbon ion energies [3]. |
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NP11.00134: SPACE: SPACE PLASMAS Session Chairs |
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NP11.00135: Space Object Identification by In Situ Measurements of Orbit-Driven Waves (SOIMOW) Paul A Bernhardt, Lauchie Scott, Andrew Howarth SOIMOW measures in situ electromagnetic plasma waves excited by satellites and space debris moving through the earth’s plasma in low earth orbit. Space debris detection is traditionally accomplished with satellite sensors employing optics and ranging radars. SOIMOW uses in situ conjunctions to measures low frequency plasma modes with electric and magnetic field receivers on host satellites. Satellites moving through the near-earth ionosphere between 200 and 1000 km altitude become electrically charged by both electron collection and photo emission in sunlight. These hypersonic charged objects pass through the ionosphere setting up electric currents and electric potentials that can produce a wide range of plasma waves. The SOIMOW technique may measure electromagnetic plasma waves launched by satellite motion out to ranges of tens of kilometers. The SOIMOW concept has been successfully demonstrated using the Radio Receiver Instrument (RRI) on the SWARM-E satellite with detection of micro-satellites and space debris in low earth orbit (LEO). Besides space object detection, the observations show how space-plasma waves affect the thermosphere and ionosphere. |
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NP11.00136: Characterizing Plasma Turbulence Using Sparse, Multi-point, Multi-scale Measurements Kristopher G Klein, Lev A Arzamasskiy, Matthew W Kunz, Jason M TenBarge, Teddy Broeren Studying the dynamic interactions of turbulent fluctuations at multiple scales as energy is transported between structures of different sizes is necessary for characterizing this universal phenomena. In preparation for selected (e.g. HelioSwarm) and proposed (e.g. Plasma Observatory) multi-spacecraft missions designed to study the multi-scale nature of turbulence in space plasmas, we extend a number of analysis techniques that have been developed and refined for single-spacecraft or single-scale missions and apply them to synthetic data drawn from numerical simulations of turbulence, using both the Gkyell and Pegasus++ simulation codes. These techniques include magnetic field reconstruction, estimations of spatial gradients, deconvolution of spatial and temporal correlation scales, and determinations of scale-dependent intermittency. The accuracy of these techniques is assessed as a function of the geometry of the inter-spacecraft separations, which provides guidance for the design of multi-spacecraft observatory trajectories. |
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NP11.00137: Ablation of Carbon Objects within the Jovian Atmosphere Christopher A Mehta, Evdokiya Kostadinova, Dmitry Orlov Here, we study the ablation of carbonaceous materials as they enter Jupiter’s atmosphere using an ablation model that solves equations for the time evolution of velocity and mass. We consider spherical objects of various initial masses and velocities and calculate ablation rates for several choices of heat transfer/ablation coefficients. Predictions from the ablation model are compared to instrumental data obtained from the Galileo Atmospheric Probe. We establish that a heat transfer coefficient of 0.1 and ablation coefficient of 81.4 MJ/kg result in similar mass loss rates as those recorded by the Galileo Probe. Lastly, considering carbonaceous materials with an ablation coefficient as low as 45.6 MJ/kg still are in agreement with past ablation studies in a reasonable approximation of ablation rates for entries in the Jovian atmosphere (80%-100% mass loss). Therefore, such materials cannot be ruled out as viable candidates for future spacecraft heat shields. Work supported by US DOE under DE-SC0022554 and DE-SC0021338. |
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NP11.00138: Surveying Machine Learning Approaches to Space Plasma Region Identification Thomas Y Chen Identifying and classifying near-Earth plasma regions is integral to understand aspects such as waves, turbulence, and magnetic reconnection. In recent years, machine learning (ML) and artificial intelligence techniques have been utilized to understand space plasma. Algorithms such as convolutional neural networks (CNNs) and self-organizing maps (SOMs) have been employed. In this work, we survey this new but nascent area of research and identify best practices for the use of ML in this scope. |
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NP11.00139: Inferring plasma conditions of the primordial solar nebula from meteorite samples Chuchu Xiang, Augusto Carballido, Joshua Holden, Romy Hanna, Lorin S Matthews, Truell W Hyde The process of planet formation consists of hierarchical growth of solid bodies spanning the scales from m-sized dust to km-sized planetesimals. The growth of solids from the sub-millimeter to meter scales is a particularly poorly understood regime in this process. Meteoritic samples show that many mm-sized inclusions (chondrules) have dust coatings, known as fine-grained rims (FGRs). FGRs may play a key role in allowing chondrules to stick together to form larger bodies. The collection of a dust rim on the chondrule surface depends on nebular conditions such as ionization of the nebular gas and turbulence. Dust grains and chondrules immersed in the plasma become charged, providing a mutually repulsive force, while turbulence provides greater relative velocities between chondrules and dust. The ratio of electrostatic potential energy to kinetic energy at the point of collision affects the subsequent rim growth. Here we report on numerical models of FGR growth and restructuring designed to link the observed FGR characteristics to the nebular conditions. |
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NP11.00140: Spectral methods for space plasma physics using Dedalus: Applications to ionospheric phenomena Enrique L Rojas, Keaton J Burns Spectral methods are well known for outstanding accuracy and scale very efficiently when simple boundary conditions are applicable and no shocks or discontinuities are expected. Numerous problems in space physics have these characteristics. In this work, I will briefly describe the "Dedalus" library for solving PDEs using spectral methods and outline some applications to ionospheric physics. We will use this library to simulate simplified, but representative phenomena such as incoherent scatter radar spectra, Farley-Buneman instabilities, equatorial plasma bubbles, and Langmuir turbulence. These problems will allow us to explore different aspects of Dedalus' versatility. Furthermore, we will outline some research questions that may be investigated using this tool. |
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NP11.00141: Generalized framework for characterizing entropy production in collisionless plasmas Vladimir V Zhdankin Collisionless plasmas develop nonthermal particle distributions after being energized, and thus relax to a state of non-maximal Boltzmann-Gibbs entropy. While the Vlasov equation predicts that Boltzmann-Gibbs entropy is formally conserved (along with an infinite set of other Casimir invariants), anomalous entropy production may be enabled by phase mixing, nonlinear entropy cascades, etc. Characterizing the nature and extent of entropy production for various irreversible processes is a basic plasma physics problem with applications to space and astrophysical systems. I describe a theoretical framework for representing entropy production via an infinite set of dimensional quantities, the "Casimir momenta", which generalize the Boltzmann-Gibbs entropy and are ideally conserved by the Vlasov equation. Evolution of the Casimir momenta characterizes violations of the Vlasov equation (and therefore irreversibility) at different energy scales. The framework is validated in particle-in-cell simulations of laminar and turbulent flows. This framework may be useful for diagnosing collisionless energy dissipation and for constructing models of nonthermal particle acceleration in systems such as the solar wind and Earth's magnetosphere. |
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NP11.00142: Energized electron signatures within standing kinetic Alfven waves in the inner magnetosphere Peter Damiano, Eun-Hwa Kim, Jay Johnson, Arthur J Hull, Simon Wing, Christopher C Chaston Standing Alfven eigenmodes with perpendicular scales on the order of the equatorial ion gyroradius are known as kinetic scale field line resonances (KFLRs) and are observed to peak at substorm onset well into the inner magnetosphere (Chaston et al., 2014). Cluster observations (Hull et al., 2021) have also illustrated that substorm auroral bead formation and currents are associated with these waves. In order to better understand the electron energization that leads to the associated auroral precipitation, we present results of multi-period simulations of KFLRs using a gyrofluid-kinetic electron model (Damiano et al., 2015) in a dipolar magnetic field topology with the inclusion of both hot magnetospheric and cold ionospheric sourced electron populations. We track the electron response at different latitudes and compare the simulation results with satellite observations. We illustrate the formation of highly field aligned electron distributions (primarily manifest in the cold electron population) that are linked to electron trapping effects and are in very good agreement with Cluster observations at mid-latitudes (Hull et al., 2021). At high latitudes, broadband electron distributions with energies reaching keV levels are evident in both upward and downward current regions that are consistent with the characteristics of energized electrons observed by the DMSP satellites. The simulations also illustrate that this electron energization is a significant sink of Alfven wave energy that can damp an undriven standing mode in a few eigenperiods. |
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NP11.00143: Enabling Optimizations for Global Magnetospheric Kinetic Simulations with Reduced Kinetic Spectral Models Oleksandr Koshkarov, Gian Luca Delzanno, Vadim S Roytershteyn, Cecilia Pagliantini Efficient coupling of the microscopic physics into the macroscopic system-scale dynamics (called "fluid-kinetic" coupling) is probably the most important and unresolved problem of computational plasma physics. It impacts most of plasma physics areas including space physics and fusion systems. Majority of conventional simulation tools capable of describing large scale dynamics are usually limited to simplified fluid/magnetohydrodynamics description of the plasma, because of the large spatial and temporal scale separation typical of plasmas. Yet, fluid models lack the microscopic physics, which is known to be important in many applications (e.g., reconnection, shock physics, etc.) A way forward is to build models that combine kinetic and fluid description in one consistent framework. The development of such methods can bridge the scale gap to successfully handle coupling of large-scale dynamics and microscopic processes. |
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NP11.00144: Characterization and comparison of an electric dipole and loop antenna impedance and efficiency in whistler wave excitement Jesus A Perez, Seth Dorfman, Patrick Pribyl, Quinn Marksteiner, Nicholas Mozyrsky, Gian Luca Delzanno, Troy Carter High energy electrons from either solar wind or from human activities may become trapped inside the Van Allen radiation belts and persist there for long periods of time. Spacecraft in the regions may be suspectable to damage from these trapped electrons. Whistler waves are known to precipitate electrons in the atmosphere, so a proposed solution is using spacecraft to carry compact electron beams or antennas to remediate the trapped electrons. Results of a laboratory plasma experiment are presented here. The purpose of the experiment is to compare the efficiency of exciting whistler waves by an electric dipole and multi-turn loop antenna. A distinguishing factor in these antennas is the ability for accurate measurements of the voltage and current right at the antenna. Characterization of the impedance and radiation resistance will allow for comparison to theory and space mission experiments. |
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NP11.00145: Particle-in-Cell Simulations of Plasma Sheath Effects on Impedance of a Whistler Antenna Operating in the Magnetosphere Kevin A Shipman, Daniil Svyatsky, Patrick Colestock, Nikolai Yampolsky, Mark A Gilmore, Quinn Marksteiner, Gian Luca Delzanno A powerful coronal mass ejection or a high-altitude nuclear explosion (HANE) can produce an artificial radiation belt containing high-energy electrons (~1MeV) in the earth's upper atmosphere that would populate its magnetosphere. Some of these high-energy electrons become trapped along the Earth's magnetic field lines and would severely damage or destroy nearly all lower-earth orbit (LEO) satellites in just a few days. Over the years, it has been of much interest to devise a scheme that remediates these MeV electrons from the magnetosphere and reduces the amount of damage caused by them. A proposed technique is to use a space-borne high-voltage dipole antenna to inject very low frequency (VLF) whistler waves (3-30kHz) along the earth's magnetic field lines to precipitate the electrons through pitch angle scattering. Because the magnetosphere is composed of plasma, a charged antenna will form a nonlinear plasma sheath around its surface. This sheath changes the input impedance of the antenna, reducing efficiency. This research uses a three-dimensional electrostatic curvilinear particle-in-cell (CPIC) code to simulate the antenna-sheath interaction to calculate the impedance induced by the sheath. We compare the numerical results to an existing analytical developed by Balmain et al. and Song et al.[1][2]. |
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NP11.00146: Interchange magnetic reconnection within coronal holes powers the solar wind James F Drake, Stuart Bale, Michael McManus, Davin Larson, Michael M Swisdak, Marco C Velli
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NP11.00147: Heliospheric Magnetic Fields Generated by Solar Wind Current Fluctuations. Charles F Driscoll The 20 years of ACE satellite measurements of B(t) at 1AU enable detailed spectral and dynamical analyses, here supplemented by radial dependencies from Ulysses and Mariner from 0.3 - 5 AU. We find: |
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NP11.00148: Electrostatic Instabilities in Highly Collisional Magnetized Plasmas with Multi-Species Ions Yakov S Dimant, Meers M Oppenheim, Samuel Evans, Juan Martinez-Sykora Collisional plasma instabilities in low-ionized, highly dissipative, weakly magnetized plasmas play an important role in the lower Earth's ionosphere and, potentially, in other planetary ionospheres. In the Solar chromosphere, macroscopic effects of collisional plasma instabilities may contribute into significant chromospheric heating --- an effect originally deduced from spectroscopic observations and relevant modeling. We have developed a unified linear theory of local plasma instabilities, such as the Farley-Buneman, electron thermal, and ion thermal instabilities, in collisional plasmas with fully or partially unmagnetized multi-species ions. Theoretical analysis, based on a simplified 5-moment multi-fluid model, produces the general linear dispersion relation for the combined instability. Important limiting cases are analyzed in detail. This analysis demonstrates the acceptable applicability of this multi-fluid model for the processes under study. Fluid model simulations usually require much less computer resources than do more accurate kinetic simulations, so that the apparent success of the fluid-model approach to the linear theory of collisional plasma instabilities makes it possible to include these small-scale instabilities (along with their possible macroscopic effects) into global fluid codes originally developed for large-scale modeling of the Solar and planetary atmospheres. |
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NP11.00149: Secondary Instabilities of Electromagnetic Ion Cyclotron Waves Associated with Cold Plasma Populations Patrick Kilian, Vadim S Roytershteyn, Gian Luca Delzanno Electromagnetic ion cyclotron (EMIC) waves are common in the Earth's inner magnetosphere, in particular during geomagnetic storms following injections of anisotropic ring current ions. These waves as well as the resulting particle scattering can strongly affect the radiation belts, and have been studied extensively. An aspect that has received comparatively much less attention is that these waves can couple very efficiently with the cold (<100 eV) particle populations of the magnetosphere. One way to do so is through secondary instabilities driven by the fact that EMIC waves induce a relative drift velocity between different plasma species which can act as a source of free energy. The properties of these instabilities (including growth rate, nonlinear saturation and energy partition) are sensitive to details of the plasma composition such as the presence of a small fraction of heavier ions, such as helium or oxygen. We will present linear theory and nonlinear simulations to show the precense and effects these secondary instabilities. |
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NP11.00150: Whistler Mode Chirped-Solitons as the Building Blocks of Chorus Chris E Crabtree, Guru Ganguli, Rualdo Soto-Chavez, Alex Fletcher Whistler mode chorus is a powerful electromagnetic emission observed in the outer radiation belts of the Earth that is an important driver of the dynamics of energetic electrons through resonant wave-particle interactions. Chorus waves are characteristically quasi-coherent and are observed as bursts of wave power called chorus elements with frequencies in the VLF range that can change on time scales of the order of tens of wave periods. Chorus elements are further subdivided into sub-elements (or sub-packets) that are characterized by a peak in the wave amplitude. We show using Bayesian spectral analysis techniques that the most probable model for the sub-elements, among the models considered, that explains the data are chirped soliton's which are solutions to the Ginzburg-Landau equation. We derive a Ginzburg-Landau equation that is applicable to whistler mode chorus and analyze analytical and numerical solutions for chirped solitons. The data and theory suggests that these chirped soliton solutions form the building blocks of chorus elements. Having an accurate model of whistler mode chorus can provide accurate models of the effects of chorus on energetic electrons. |
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NP11.00151: Gyrokinetic simulations of electromagnetic turbulence in a dipole configuration Ryusuke Numata It is well known that plasmas in the planetary magnetospheres are confined due to the inward pinch phenomenon whereby particles are transported against the density gradient. Turbulent transport due to the electrostatic entropy mode can be a possible mechanism for the inward pinch. Gyrokinetic simulations of the entropy mode in dipole configuration have successfully demonstrated the existence of a particle pinch regime [Kobayashi et al (2010)]. However, the observed plasmas in RT-1 magnetospheric experiments [Saitoh et al. (2014)] and in the planetary magnetospheres are generally high-beta, therefore electromagnetic effects may play roles in determining turbulent transport. In this work, we extend the studies of turbulent transport in a dipole configuration to high-beta plasmas. We perform gyrokinetic simulation using GS2 code and discuss how the electromagnetic effects change the transport properties. |
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NP11.00152: Energy Transfer in a High Beta MHD Turbulent Cascade Waverly Gorman, Kristopher G Klein The Howes et al. 2008 model for a MHD turbulent cascade assumes local nonlinear energy transfer and critical balance between the linear propagation and nonlinear interaction times to construct a steady-state cascade of energy from inertial through dissipation scales terminated by Landau damping. This model quantifies the bifurcation of energy between ions and electrons in solar system and astrophysical plasmas. The linear solutions for low-frequency kinetic Alfven waves have a gap where the frequency drops to zero for a proton plasma beta greater than approximately 30; this gap increases in width for increasing values of the plasma beta. Assuming only local nonlinear energy transfer, the energy cascade should halt once it reaches the gap. In this study, we investigate the Weakened Cascade model by Howes et al. 2011 that allows for non-local contributions to the cascade by including effects of shearing and diffusion, to properly model nonlinear energy transfer across the gap. We compare results for proton and electron heating from this model to direct numerical results by Kawazura et al. 2019. This update will be relevant for a variety of heliospheric and astrophysical systems with a proton plasma beta larger than 30. |
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NP11.00153: Beyond bi-Maxwellians: The Influence of Non-Equilibrium Features on the Development of Microinstabilities in Solar Wind Plasma Waves Jada Walters, Kristopher G Klein, Ben Chandran, Michael L Stevens, Daniel Verscharen, Emily R Lichko The hot and low-density solar wind plasma is a weakly collisional system, and thus a variety of non-equilibrium features can develop in velocity distribution functions (VDFs) and are observed in the solar wind. When examining plasma waves in the solar wind, typical treatment of proton VDFs involves modeling them with simplified bi-Maxwellian fits. While this simplification makes the calculation of plasma response straight-forward, it may also cause us to neglect microinstabilities triggered by non-equilibrium features or their impact on suppression or enhancement of waves. As microinstabilities are important to the processes that transfer energy at large MHD scales and dissipate them at smaller kinetic scales in collisionless plasmas, we wish to accurately model them using observed solar wind proton VDFs. In this work, we investigate how deviations from a two-component bi-Maxwellian VDF affect the onset and evolution of parallel-propagating microinstabilities associated with solar wind protons. We use the Arbitrary Linear Plasma Solver (ALPS) numerical dispersion solver to find the real frequencies, growth/damping rates, and wave eigenfunctions of the Alfvén and fast modes using proton VDFs extracted from Wind spacecraft observations. We compare this wave behavior to that obtained by applying the same procedure to core-and-beam bi-Maxwellian fits of the Wind proton VDFs. We find several significant differences in the plasma waves obtained for the data and bi-Maxwellian fits, including both the driving and suppression of instabilities in the data compared to the model. By application of the quasi-linear diffusion operator to our VDFs, we pinpoint resonantly interacting regions in velocity space where differences between the model and data VDF are seen to significantly affect the plasma wave behavior. |
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NP11.00154: Transit-Time Damping Signatures in Solar Wind Turbulence Simulations Rui Huang, Gregory G Howes, Andrew J McCubbin Understanding the physical mechanisms of the damping of the turbulent fluctuations has broad applications to the study of many astrophysical plasmas. At the dissipation range, the in situ measurements bring particular challenges, for example, integration over a spatial volume is not possible with only data at a single point available for single spacecraft. The problem can be solved by employing the field-particle correlation (FPC) technique to isolate the secular energy transfer from turbulent electromagnetic fields to the plasma particles and track down the unique velocity-space signature for each physics process. Landau damping (LD) and transit-time damping (TTD) are both possible mechanisms. Previous work has revealed the velocity-space signature of LD. In this research, the key physics of TTD is extracted by working through the limit of the Vlasov-Maxwell dispersion relation. The velocity-space signature of TTD and the comparison with that of LD is demonstrated. The simulation code AstroGK is applied to carry out both linear and turbulent runs, and the examination of the simulated results illustrates the varied contributions of TTD under different initial settings. This work provides a detailed study of TTD and helps gain scientific insights into the turbulent damping. |
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NP11.00155: Investigation of Shear-Driven Electron-Ion Hybrid Scale Instabilities at Dipolarization Fronts Landry Horimbere Dipolarization fronts are regions of stressed plasma that are suspected to be the source of broadband electrostatic and electromagnetic noise in the Earth's magnetosphere. It has been posited that after highly impulsive reconnection events, they can develop an electric field and shear layer with gradient length scales smaller than the ion gyroradius. Researchers at the Naval Research Laboratory (NRL) have developed a model for the spectrum of electrostatic and electromagnetic waves that are produced by the Electron-Ion Hybrid (EIH) instabilities of such a compressed front. In this work, I analytically calculate the dispersion relations for the Kelvin-Helmholtz (KH) and electrostatic EIH instability for both a single piecewise continuous shear layer and a piecewise continuous symmetric double shear layer (jet). I find that both the KH and EIH modes exhibit instabilities at arbitrarily low velocities but that the wavelength of the fastest-growing EIH mode also diverges at low-velocity shears. |
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NP11.00156: Fast Magnetic Reconnection induced by Resistivity Gradients Yi-Hsin Liu, Shan-Chang Lin, Xiaocan Li Using 2-dimensional (2D) magnetohydrodynamics (MHD) simulations, we show that Petschek-type magnetic reconnection can be induced using a simple resistivity gradient in the reconnection outflow direction, revealing the key ingredient of steady fast reconnection in the collisional limit. We find that the diffusion region self-adjusts its half-length to fit the given gradient scale of resistivity. The induced reconnection x-line and flow stagnation point always reside within the resistivity transition region closer to the higher resistivity end. The opening of one exhaust by this resistivity gradient will lead to the opening of the other exhaust located on the other side of the x-line, within the region of uniform resistivity. Potential applications of this setup to reconnection-based thrusters and solar spicules are discussed. In a separate set of numerical experiments, we explore the maximum plausible reconnection rate using a large and spatially localized resistivity right at the x-line. Interestingly, the resulting current density at the x-line drops significantly so that the normalized reconnection rate remains bounded by the value ≃ 0.2, consistent with the theoretical prediction.
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NP11.00157: Kinetic modeling of the dynamic nature of Lunar Mini-Magnetospheres Adam J Stanier, Li-Jen Chen, Ari Le, Jasper Halekas As the solar wind plasma collides with the moon, particles are absorbed causing a deep density void on the downstream side. Due to the lack of a global magnetic dipole, the interplanetary magnetic field largely passes through the moon with only weak perturbation due to pressure balance across the wake. However, this simple picture is complicated by the presence of localized crustal magnetic anomalies that are scattered over the surface of the moon. Spacecraft orbiting closely over the surface have found shock-like compressions and electromagnetic activity both upstream of these anomalies and downstream along the edges of the wake. The basic plasma physics of these processes is interesting as the stand-off distance of the crustal anomalies is often less than the ion skin depth and gyro-radius. |
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NP11.00158: MMS Observations of Compressed Current Sheets: Importance of the Ambipolar Electric Field Ami M DuBois, Chris E Crabtree, Guru Ganguli Micro-scale features are now being resolved by NASA's Magnetospheric Multi-Scale (MMS) mission, which means for the first time, we are able to investigate thin current sheets in detail and assess their role in magnetic reconnection. Our analysis of kinetic-scale structures and dynamics associated with compressed current sheets in MMS data shows that a transverse ambipolar electric field is localized to the region of lower hybrid fluctuations and the pressure gradient is comparatively small, leading to the interpretation that E×B velocity shear is the underlying fluctuation driving mechanism. The presence and location of shear-driven waves at the center of current sheets is notable because laboratory experiments and PIC simulations have shown that shear-driven lower hybrid fluctuations are capable of producing significant anomalous cross-field transport and resistivity, which can trigger magnetic reconnection. We can calculate the anomalous resistivity directly and show that the resistivity is significant. Finally, we show that the electron distribution function is non-gyrotropic (generated by a quasi-static electric field), which theoretical arguments suggest is an indicator of the possibility for magnetic reconnection to occur. |
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NP11.00159: Machine Learning Algorithms for the Detection of Plasmoids in Multiple-X-Line Collisionless Reconnection Regions Kendra A Bergstedt, Hantao Ji Correctly identifying structures in multiple-X-line reconnection regions is crucial for understanding the physics of the coupling of the microscale to the macroscale, such as the potential role that the plasmoid instability plays in reconnection dynamics and energy transfer. One specific area of research where this is important is the study of naturally occurring reconnection regions in Earth's magnetotail via analysis of in-situ data from spacecraft. A limitation of this data is that spacecraft can only sample a single point in space for each timestep, and trace a 1D path through the plasma. This limitation makes detection and identification of dynamic plasma structures difficult, especially if the plasma is sampled by only a single spacecraft. Techniques such as identifying structures by eye and by fitting to mathematical models are commonly and effectively used, but neither is suitable for the detection of large numbers of structures which are stretched or warped from their idealized shape. Previous work tackling this methodological problem used simple hand-tuned algorithms for detection and classification (Bergstedt et al. 2020). This work develops a more nuanced and robust detection algorithm which utilizes a set of simulated 'spacecraft' trajectories through 2D PIC simulations of reconnection to train a machine learning model to identify regions of data corresponding to plasmoids. The results from a simple binary classifier based on a 1D Convolutional Neural Network (CNN) architecture are presented and evaluated. Potential applications of the classifier are discussed. |
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NP11.00160: A Study of the Electron Cyclotron Drift Instability with Solar Wind Particle Distributions Jason M TenBarge, James Juno, Kristopher G Klein, Gregory G Howes The electron cyclotron drift instability (ECDI) is often observed in the foot of heliospheric shocks and plays an important role in heating electrons and ions in collisionless shocks, as well as supplying anomalous resistivity. Although commonly observed in quasi-perpendicular interplanetary shocks and Earth's bowshock, the ECDI is a challenging instability to study in self-consistent particle-in-cell simulations of shocks, and isolated studies of the ECDI have generally been limited to simple geometries and initial conditions. Here, we present a study of the ECDI with a variety of initial conditions relevant to shocks by employing the fully non-linear continuum Vlasov-Maxwell solver within the Gkeyll simulation framework. By drawing from in situ solar wind data, we employ realistic particle distributions to examine how deviations from an initial Maxwellian alter the growth of the instability and subsequent particle energization. |
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NP11.00161: Understanding the Impact of Instabilities on the Particle Energization in Collisionless Shocks Collin R Brown, Gregory G Howes, Kristopher G Klein, James Juno, Colby C Haggerty Understanding the kinetic mechanisms and instabilities present in collisionless shocks is critical to examining particle energization in the local heliosphere and in the galaxy at large. Using the field-particle correlation technique and the novel instability isolation method, we have developed tools for understanding phase-space energization of individual mechanisms in hybrid PIC simulations of moderately supercritical quasi-perpendicular and oblique shocks. The instability isolation method is used to separate out individual mechanisms present in simulations of shocks and has had success with isolating and identifying the wave launched by the corrugation instability, which ripples the surface of shocks. We use the field-particle correlation technique with this isolated mode to produce velocity-space signatures of the instability that show the transfer of energy between fields and particles in phase-space due to just the instability itself. Here, we use linear Vlasov-Maxwell theory to predict these velocity-space signatures of the instability. Making successful predictions using linear theory is desired to solidify our understanding of the transfer of energy in the full six dimensions of phase-space. |
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NP11.00162: Electron heating along the separatrix due to whistler waves in asymmetric magnetic reconnection seung choi, Naoki Bessho, Li-jen Chen, Shan Wang, Michael Hesse Magnetic reconnection is one of the important energy conversion processes in collisionless plasma. Using 2-D particle-in-cell (PIC) simulations of asymmetric guide field reconnection (30% of the reconnecting magnetic field), we investigate wave-particle interactions in the magnetosphere side of the separatrix, outside the electron diffusion region. 2-D plots of the energy conversion term in the Poynting equation show that there is a strong energy conversion between waves and particles along the separatrix. Large-amplitude whistler waves are generated along the separatrix by two mechanisms: one is the electron cyclotron resonance due to an anisotropic high-speed electron beam, and the other is the Landau resonance due to a hot slow electron beam [Choi et al. 2022]. 2-D plots of parallel and perpendicular electron temperatures show modulation along the separatrix, which matches the wave pattern of the whistler wave. Performing particle tracing in the simulation, we investigate how electrons are energized by the whistler wave along the separatrix. Some electrons show energy increase with modulation whose frequency is similar to the wave frequency, suggesting that electrons are energized by the wave-particle interaction with the whistler wave. |
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NP11.00163: Model for large scale electron heating applied to MMS observations in the Earth's magnetotail. Jan Egedal Magnetic reconnection is the process by which stress in the field of a magnetized plasma is reduced by a topological rearrangement of its magnetic-field lines. In the Earth’s magnetotail, reconnection energizes electrons up to hundreds of keV and solar-flare events can channel up to 50% of the magnetic energy into the electrons, resulting in superthermal populations in the MeV range. Using kinetic simulations it has been shown that magnetic-field aligned electric fields can be present over large spatial scales in reconnection exhausts [1,2]. The largest values of E|| are observed within double layers. The electron confinement allows sustained energization by perpendicular electric fields. The energization is a consequence of the confined electrons’ chaotic orbital motion that includes drifts aligned with the reconnection electric field. The mechanism is effective in an extended region of the reconnection exhaust allowing for the generation of superthermal electrons in large scale reconnection scenarios, including those with only a single x-line. The model is applied to new observations by the NASA’s MMS mission of large scale electron heating during reconnection in the Earth’s magnetosphere [3]. |
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NP11.00164: 2D Reconstruction of magnetotail EDR measured by MMS Jack M Schroeder, Jan Egedal, Giulia Cozzani, Yuri Khotyaintsev, William S Daughton, Richard Denton, James L Burch Models for collisionless magnetic reconnection in near-Earth space are distinctly characterized as 2D or 3D. In 2D kinetic models, the frozen-in law for the electron fluid is usually broken by laminar dynamics involving structures set by the electron orbit size while in 3D models the width of the electron diffusion region is broadened by turbulent effects. We present an analysis of in situ spacecraft observations from the Earth’s magnetotail of a fortuitous encounter with an active reconnection region, mapping the observations onto a 2D spatial domain. While the event likely was perturbed by low-frequency 3D dynamics, the structure of the electron diffusion region remains consistent with results from a 2D kinetic simulation. As such, the event represents a unique validation of 2D kinetic, and laminar reconnection models. |
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NP11.00165: Using Machine Learning to Locate Three-Dimensional Magnetic Reconnection within PHASMA Gabriela Himmele, Regis John, Thomas Rood, Peiyun Shi, Sonu Yadav, Earl Scime, Paul A Cassak The PHASMA (PHAse Space MApping) facility at WVU uses pulsed plasma guns to investigate magnetic reconnection through the interaction of two magnetic flux ropes. This study makes use of parameters such as the squashing factor and the Quasi-Separatrix Layer (QSL) to identify and locate magnetic reconnection within PHASMA. Based on these parameters, we attempt to predict where magnetic reconnection occurs at a distant location based on a predictive neural network that uses nonlocal (edge) magnetic measurements and line-integrated fast photodiode measurements in PHASMA. Initial validation of the machine learning algorithm was performed on magnetic field data from the Large Plasma Physics Device (LAPD) at the UCLA Basic Science Plasma Facility. This analysis will enable new studies of reconnection in highly turbulent and irreproducible systems by providing a means of localizing the time and location of reconnection to better synchronize triggered measurements, such as Thomson scattering measurements of the electron velocity distribution functions. |
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NP11.00166: 3D Simulations of Reconnection Spreading Between Non-Parallel Flux Ropes in the WVU PHASMA Experiment Regis John, Paul Cassak, Peiyun Shi, Sonu Yadav, Earl Scime Magnetic flux ropes are columns of plasma with axial and azimuthal magnetic fields and are commonly observed on the Sun and in the terrestrial magnetosphere. Two flux ropes are created with pulsed plasma guns in the West Virginia University PHAse Space MApping (PHASMA) experiment. The flux ropes are fixed in space at one end (the plasma gun end) and the other end of the ropes terminates on a conical anode. By varying the angle of the cone, the boundary condition is variable from line-tied (fixed) to non-line-tied (free). The conical anode introduces a small degree of tilt between the two flux ropes. In the experiment, the flux ropes are observed to rotate around each other, merge, and bounce during which magnetic energy is released via the process of magnetic reconnection. Here, we present simulation results from the 3D electron-magnetohydrodynamics (EMHD) code F3D of reconnecting flux ropes tilted at an angle, motivated by the experiment. We find reconnection spreads sequentially in a zipper-like fashion starting where the flux ropes are initially closest and cascading along the axial direction to where the flux ropes began further apart. We perform a parametric study as a function of flux rope axial current, axial magnetic field, and boundary conditions (line-tied and non-line-tied) and compare them to the laboratory observations. |
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NP11.00167: Argon ion temperature evolution in magnetic reconnection Matthew J Lazo, Mitchell C Paul, Thomas E Steinberger, Peiyun Shi, Ripudaman S Nirwan, Sonu Yadav, Earl Scime Laser induced fluorescence (LIF) measurements were conducted during magnetic reconnection of two argon plasma flux ropes in the PHAse Space MApping (PHASMA) experiment. The flux ropes are generated using two plasma guns. A pulsed laser was used to induce LIF near the separatrix at several wavelengths for an ensemble of reproducible gun shots. Signal over several shots at one wavelength is then averaged together to determine the magnitude of the ion velocity distribution function (IVDF) at a single wavelength. The process is repeated for 20 wavelengths to build up a discrete IVDF at a particular time during reconnection. A fit to the measured IVDF provides a measure of the ion temperature and the bulk ion flow. This process is repeated for several times throughout the reconnection event to determine ion temperature evolution in time. The ion temperature magnitude and evolution is discussed in the context of electron temperature measurements from the PHASMA Thomson scattering system, Langmuir triple probe, and retarding field energy analyzer measurements. We also discuss different methods for processing the LIF time series measurements to obtain the IVDF magnitude. |
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